Standard POP3 port. Setting up mail via POP3
This article covers the most commonly used protocols Email on the Internet - POP3, IMAP and SMTP. Each of them has a specific function and way of working. The content of the article explains which configuration is best suited for the user's specific needs when using an e-mail client. It also reveals the answer to the question of what protocol e-mail supports.
What is POP3?
Protocol Version 3 (POP3) is a standard email protocol used to receive email from a remote server to a local one. mail client. Allows you to download messages to your local computer and read them even if the user is in offline mode. Please note that when you use POP3 to connect to your account, messages are downloaded locally and deleted from the email server.
By default, the POP3 protocol runs on two ports:
port 110 is an unencrypted POP3 port;
port 995 - this should be used if you want to connect to POP3 securely.
What is IMAP?
Internet Message Access Protocol (IMAP) is a protocol for receiving email messages, used to access email on a remote web server from a local client. IMAP and POP3 are the two most commonly used protocols for receiving emails and are supported by all modern email clients and web servers.
The POP3 protocol means that your email address is accessible only from one application, while IMAP allows simultaneous login from several clients at once. This is why IMAP is better if you're going to be accessing your email from different places or if your messages are managed by multiple users.
The IMAP protocol runs on two ports:
port 143 is the default unencrypted IMAP port;
port 993 - this must be used if you want to connect securely using IMAP.
What is SMTP?
The protocol is standard protocol to send email over the Internet.
SMTP operates on three ports:
port 25 is unencrypted by default;
port 2525 - this is opened on all SiteGround servers if port 25 is filtered (for example by your ISP) and you want to send unencrypted emails using SMTP;
port 465 - This is used if you want to send messages securely using SMTP.
What protocols are used to exchange email? Concepts and terms
The term email server refers to the two servers required to send and receive emails, i.e. SMTP and POP.
The incoming mail server is the server associated with your email address account. It cannot have more than one incoming mail server. To access incoming messages, you need an email client—a program that can receive email from an account, allowing the user to read, forward, delete, and reply to messages. Depending on your server, you may be able to use a dedicated email client (eg. Outlook Express) or web browser. So, Internet Explorer used to access email-based accounts. Messages are stored on the incoming mail server until it is downloaded. Once you have downloaded your mail from the mail server, you cannot do it again. To successfully download data, you must enter correct settings in an email program. Most incoming mail servers use one of the following protocols: IMAP, POP3, HTTP.
Outgoing mail server (SMTP)
This is a server used only for sending emails (to transfer them from your email client program to the receiver). Most outgoing mail servers use Protocol) to send correspondence. Depending on your network parameters The outgoing mail server may belong to your ISP or the server where you set up your account. Alternatively, you can use a subscription-based SMTP server that will allow you to send emails from any account. Due to spam issues, most outgoing email servers do not allow you to send emails unless you are logged into their network. A server with an open relay will allow you to use it to send emails, regardless of whether you belong to it network group or not.
Email Ports
For networks, a port means the end point of a logical connection. The port number determines its type. The following are the default email ports:
POP3 - port 110;
IMAP - port 143;
SMTP - port 25;
HTTP - port 80;
secure SMTP (SSMTP) - port 465;
secure IMAP (IMAP4-SSL) - port 585;
IMAP4 over SSL (IMAPS) - port 993;
Secure POP3 (SSL-POP) - port 995.
Email protocols: IMAP, POP3, SMTP and HTTP
Basically the protocol refers to standard method, used at each end of the communication channel. To deal with email, you must use a special client to access the mail server. In turn, they can exchange information with each other using completely different protocols.
IMAP protocol
IMAP (Internet Message Access Protocol) is a standard protocol for accessing email from your local server. IMAP is a client/server protocol in which email is received and data is stored by your Internet server. Since it only requires a small data transfer, it works well even with slow connection, for example, when connecting using a modem. When attempting to read a particular email message, the client downloads data from the server. You can also create and manage folders or mailboxes on the server, delete messages.
POP3 protocol
POP (Post Office Protocol 3) e-mail provides a simple, standardized way for users to access their mailboxes and download messages to their computers.
When using the POP protocol, all your email messages will be downloaded from the mail server to your local computer. You can also leave copies of your emails on the server. The advantage is that after downloading your messages, you can disconnect your Internet connection and read your email at your leisure without incurring additional communication costs. On the other hand, with this protocol you receive and download a lot unwanted messages(including spam or viruses).
SMTP protocol
The protocol is used by the Mail Transfer Agent (MTA) to deliver emails to a specific recipient server. SMTP can only be used to send emails, not to receive them. Depending on your network or ISP settings, you may only be able to use the SMTP protocol under certain conditions.
HTTP protocols
HTTP is not a protocol designed for email communication, but it can be used to access your mailbox. It is also often called web email. It can be used to compose or receive emails from your account. Hotmail - good example using HTTP as an email protocol.
Managed File Transfers and Network Solutions
Your ability to send and receive email is mainly due to three things: TCP protocols. They are SMTP, IMAP and POP3.
SMTP
Let's start with SMTP because its main function is different from the other two. SMTP, or Simple Mail Transfer Protocol, is primarily used to send email from an email client (such as Microsoft Outlook, Thunderbird, or Apple Mail) to an email server. It is also used to relay or forward mail messages from one mail server to another. This is necessary if the sender and recipient have different email service providers.
SMTP, which is specified in RFC 5321, uses port 25 by default. It can also use port 587 and port 465. The latter, which was introduced as the port of choice for secure SMTP (a.k.a. SMTPS), is considered deprecated. But in fact, it is still used by several email service providers.
POP3
Post Office Protocol, or POP, is used to retrieve email messages from Latest version The one that is widely used is version 3, hence the term "POP3".
POP version 3, specified in RFC 1939, supports extensions and several authentication mechanisms. Authentication features are required to prevent malicious users from accessing user communications.
The POP3 client receives email as follows:
connects to the mail server via port 143 (or 993 for SSL/TLS connections);
retrieves email messages;
serves to connect before closing the mail client application and download messages on demand.
connects to the mail server on port 110 (or 995 for SSL connections/TLS);
deletes copies of messages stored on the server;
disconnects from the server.
Although POP clients can be configured to allow the server to continue to store copies of downloaded messages, the steps described above are common practice.
IMAP
IMAP, especially Current version(IMAP4), is a more complex protocol. This allows users to group related messages and place them in folders, which in turn can be organized hierarchically. It is also equipped with message flags that indicate whether the message has been read, deleted, or received. It even allows users to search server mailboxes.
Operation logic (imap4 settings):
Please note that messages are not deleted on the server. This can have serious consequences. IMAP specifications can be found in RFC 3501.
Choosing between IMAP and POP3
Since the basic function of SMTP is fundamentally different, the choice dilemma better protocol usually only includes IMAP and POP3.
If server storage space is important to you, then choose POP3. A server with limited memory is one of the main factors that may force you to support POP3. Because IMAP leaves messages on the server, it can consume memory space faster than POP3.
If you want to access your mail at any time, then it is better to stick with IMAP. There is one good reason, which is why IMAP was designed to store messages on a server. It is used to search for messages from multiple devices - sometimes even simultaneously. So if you have an iPhone, Android tablet, laptop and desktop and you want to read email from any or all of these devices, then IMAP will be the best choice.
Synchronization is another advantage of IMAP. If you access email messages from multiple devices, you'll likely want them all to show any activity you've performed.
For example, if you read messages A, B, and C, you want them to also be marked as read on other devices. If you have deleted letters B and C, then you will want the same messages to be deleted from your inbox on all gadgets. All these synchronizations can only be achieved if you use IMAP.
Since IMAP allows users to organize messages hierarchically and place them in folders, it helps users better organize their correspondence.
Of course, everything functionality IMAPs come at a price. These solutions are more difficult to implement and the protocol ends up consuming a lot more CPU and RAM, especially when it performs the synchronization process. Actually high load CPU and memory drain can happen on both the client and server side if there are a ton of messages to sync. From this point of view, the POP3 protocol is less expensive, although less functional.
Privacy is also one of the issues that will greatly depend on the end users. They would generally prefer to download all email messages and not leave copies of them on an unknown server.
Speed is an advantage that varies and depends on the situation. POP3 has the ability to download everything mail messages when connected. And IMAP can, if necessary (for example, when there is insufficient traffic), download only message headers or certain parts and leave attachments on the server. Only when the user decides that the remaining parts are worth downloading will they become available to him. Therefore, IMAP can be considered faster.
However, if all messages on the server must be downloaded every time, then POP3 will be much faster.
As you can see, each of the described protocols has its own advantages and disadvantages. It's up to you to decide which features or capabilities are more important.
Also, the desired method of accessing the e-mail client determines the preferred protocol. Users who work from only one machine and use webmail to access their new emails, will appreciate POP3.
However, users who share mailboxes or access their emails from different computers will prefer IMAP.
Spam firewalls with SMTP, IMAP and POP3
Most spam firewalls only deal with and protect the SMTP protocol. The servers send and receive SMTP email and these will be checked by the spam firewall on the gateway. However, some spam firewalls provide the ability to protect POP3 and IMAP4 when external users need these services to access their email.
SMTP firewalls are transparent to end users; There are no configuration changes for clients. Users still receive and send email messages to the email server. Thus, Exchange or Dominos must configure routing of messages to the firewall based on a proxy server when sending email, and also provide the ability to send emails from the firewall.
You can work with letters not only through the Yandex.Mail web interface, but also using various email programs installed on your computer.
Configure the program using the IMAP protocol
When using the protocol IMAP mail the program synchronizes with the server and saves the folder structure of your mailbox. The letters you send through your email program will be stored not only on your computer, but also on the server, and you will be able to access them from various devices.
Before setting up mail program enable the IMAP protocol:
To configure an email program using the IMAP protocol, you must specify the following information:
Incoming mail
- connection security - SSL;
- port - 993.
- connection security - SSL;
- port - 465.
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IMAP protocol support will be enabled automatically the first time you log in to your email program.
When using the POP3 protocol, all letters from the folders that you specify in the menu Settings → Mail programs, will be saved by the email program to your computer in the Inbox folder. If necessary, you can set up filters in your email program to automatically move emails to required folders. Emails you send will only be stored on your computer.
Note. When downloading emails from a server using the POP3 protocol, Yandex.Mail automatically saves copies of emails on the server, but you can delete emails manually using the web interface. If you want to delete emails using an email program, use the IMAP protocol.
Before setting up your email program, enable the POP3 protocol:
To configure an email program using the POP3 protocol, you must specify the following information:
Incoming mail
- connection security - SSL;
- port - 995.
- mail server address - smtp.yandex.ru;
- connection security - SSL;
- port - 465.
To access the mail server, enter your Yandex username and password (or if you included two-factor authentication) . If you set up receiving mail from a mailbox like “login@yandex. ru », the login is the part of the address before the “@” sign. If you use, you must specify the full mailbox address as your login.
You can configure to receive emails via POP3 from any folder, including Spam. To do this, open the menu Settings → Mail programs and mark the required folders.
When mailbox contents are downloaded by email programs, emails are not marked as read by default. If you want to mark received emails as read, enable the appropriate option.
Problems with the mail program
This step by step guide will help you solve problems related to your email program.
Select an issue:
What message did you receive?
If a message appears about no connection to the server, try logging into Yandex.Mail with the same username and password that you use in the program. Enter your username and password manually, without using those stored in the browser.
Make sure that the protocol you want to use is enabled in the Mail programs settings section.\n
Make sure that you have specified exactly\\n in your mail program settings following parameters servers:\\n \\n \\n
If you are using IMAP
- \\n
- mail server address - imap.yandex.ru; \\n
- connection security - SSL; \\n
- port - 993. \\n
- \\n
- mail server address - smtp.yandex.ru; \\n
- connection security - SSL; \\n
- port - 465. \\n
\\n \\n \\n \\n
If you are using POP3
\\n \\n \\n Incoming mail \\n \\n
- \\n
- mail server address - pop.yandex.ru; \\n
- connection security - SSL; \\n
- port - 995. \\n
- \\n
- mail server address - smtp.yandex.ru; \\n
- connection security - SSL; \\n
- port - 465. \\n
\\n \\n \\n \\n\\n
For more information on how to check server settings in different mail programs, see the section.
\\n ")]))\">
Make sure that in your mail program settings you have accurately specified\nthe following server parameters:
If you are using IMAP
- \n
- mail server address - imap.yandex.ru; \n
- connection security - SSL; \n
- port - 993. \n
- \n
- mail server address - smtp.yandex.ru; \n
- connection security - SSL; \n
- port - 465. \n
\n \n \n \n
If you are using POP3
\n \n \n Incoming mail \n \n
- \n
- mail server address - pop.yandex.ru; \n
- connection security - SSL; \n
- port - 995. \n
- \n
- mail server address - smtp.yandex.ru; \n
- connection security - SSL; \n
- port - 465. \n
\n \n \n \n\n
Encryption of transmitted data.
\n\n ")]))">
Make sure that the protocol you want to use is enabled in the settings section.
Make sure that in the mail program settings you have accurately specified\n the following server parameters:\n \n \n
If you are using IMAP
\n \n \n Incoming mail \n \n
- \n
- mail server address - imap.yandex.ru; \n
- connection security - SSL; \n
- port - 993. \n
- \n
- mail server address - smtp.yandex.ru; \n
- connection security - SSL; \n
- port - 465. \n
\n \n \n \n
If you are using POP3
\n \n \n Incoming mail \n \n
- \n
- mail server address - pop.yandex.ru; \n
- connection security - SSL; \n
- port - 995. \n
- \n
- mail server address - smtp.yandex.ru; \n
- connection security - SSL; \n
- port - 465. \n
\n \n \n \n\n
For more information on how to check server settings in different mail programs, see the section Encrypting transmitted data.
\n ")]))">
Make sure that in your mail program settings you have accurately specified the following server parameters:
If you are using IMAP
Incoming mail
- mail server address - imap.yandex.ru;
- connection security - SSL;
- port - 993.
- mail server address - smtp.yandex.ru;
- connection security - SSL;
- port - 465.
If you are using POP3
Incoming mail
- mail server address - pop.yandex.ru;
- connection security - SSL;
- port - 995.
- mail server address - smtp.yandex.ru;
- connection security - SSL;
- port - 465.
For more information on how to check server settings in different email programs, see the section Encrypting transmitted data.
If the "Authentication required" message appears, "Sender address rejected: Access denied" or “Send auth command first”, authorization on the Yandex SMTP server is disabled in the mail program settings. Make sure the option is enabled User Authentication(for Outlook Express) or SMTP Authentication(For The Bat!).
If a message appears "Sender address rejected: not owned by auth user", the address from which you are trying to send a letter does not match the one under whose login you are authorized on the SMTP server. Make sure that in the mail program settings, the return address is set to exactly the address from which the login is used in the SMTP authorization settings.
If a message appears "Login failure or POP3 disabled", the mail program cannot access the mailbox using the POP3 protocol. Make sure you have entered correct password from the mailbox and in the settings section, access via the POP3 protocol is enabled.
If a message appears "Message rejected under suspicion of SPAM", the contents of your email were recognized by Yandex.Mail as spam. To solve the problem, open Yandex.Mail and send any one letter as a test. This way you will prove to the system that the letters are not being sent by a robot.
Check your computer for viruses using free antivirus programs: CureIt! from Dr.Web and Virus Removal Tool from Kaspersky Lab.If your mail program does not accept or send letters, check that your mail program settings are correct, as well as your computer’s Internet connection settings.
If you are using antivirus program, firewall or proxy server, disable them and check if this reproduces the problem.
Read step by step instructions to search for missing letters. Before starting work .
Select an issue:
When you delete messages, they go to the Deleted Items folder and are stored there for 30 days. During this period you can restore them:
- Go to the Deleted Items folder.
- Highlight necessary letters.
- Click the To Folder button.
If more than a month has passed since they were deleted, it will not be possible to restore the letters - they have been permanently deleted from the Yandex.Mail servers.
If the letters are not in the folder where they should be, then most likely they ended up in another folder, for example in Deleted Items or Spam. If you remember the sender's name or address, part of the text of the letter or the subject, try searching for letters in all the folders in your mailbox.
Have you found the letters?
You can restore letters:
- Go to the folder in which the letters were found.
- Select the required letters.
- Click the To Folder button.
- Select from the list the folder where you want to move the letters - for example, Inbox.
Why emails disappear and how to avoid it
The Deleted emails folder is stored for 30 days, and the Spam folder for 10 days. After this, they will be permanently deleted from Yandex servers. Why can emails end up in these folders without your knowledge:
Another user has access to your mailbox
Emails can be deleted by a user who has access to your mailbox: perhaps you forgot to end your session after working on someone else's device. To end your session, click the link in your account menu Log out on all devices. This can also be done on the page - using the link Log out on all computers.
Letters disappear in the mail program
configure the program using the POP3 protocol
A rule has been configured that deletes or moves letters. Letters disappear in the mail program.
If you use a mail program and delete letters in it, they disappear on . This happens because your program is configured using the IMAP protocol - in this case, the mailbox structure on the service is synchronized with the mailbox structure in the program. To delete messages only in the program, but leave them in Yandex.Mail, you can configure the program using the POP3 protocol, but we recommend not doing this: the messages may not synchronize correctly with the server.
A rule has been configured that deletes or moves emails Indicate authentic ones in Yandex.Passport and link them to your account. Our security system may have found your account suspicious and blocked your mailbox. Most often, this happens due to the fact that the phone number is not attached to the box or the Passport contains a fictitious first and last name. It usually takes a couple of hours to remove the lock.
If you delete letters in your mail program, but they are still in their folders on the Yandex.Mail website, then most likely your mail program is configured using the POP3 protocol. Due to the peculiarities of the POP3 protocol, messages in the mail program may not synchronize correctly with the server. To work with Yandex.Mail, it is recommended to use the IMAP protocol. To learn how to migrate your email program from POP3 to IMAP, see Migration from POP3.
If your email program does not display sent emails, then most likely your email program is configured using the POP3 protocol. Due to the peculiarities of the POP3 protocol, messages in the mail program may not synchronize correctly with the server. To work with Yandex.Mail, it is recommended to use the IMAP protocol. To learn how to migrate your email program from POP3 to IMAP, see Migration from POP3.
The report always indicates the reason for non-delivery. About the most common reasons can be read in the article web/letter/create.html#troubleshooting__received-report.
If you receive errors about an incorrect certificate when activating SSL encryption in your email program, make sure that your email program and operating system configured correctly:
- On a computer (without lags and "date from the future"). If installed wrong date, the system erroneously determines that the certificate has not yet expired or has already expired.
- All installed.
- Checking HTTPS connections is disabled in your antivirus settings. You can change your antivirus settings according to our instructions for Kaspersky Internet Security and ESET NOD32 Smart Security See the Security Certificate Errors section.
Manually add a certificate to the list of trusted certificates (Windows)
Attention. If you are not sure that you can install the certificate yourself, contact a specialist.
To add a certificate to the list of trusted certificates:
- Download the certificate. (If the linked file opens directly in your browser, click CTRL + S and save the file to your computer; there is no need to copy text from the file.)
- Open the Start menu.
- In the search field, enter certmgr.msc and click Enter key.
- In the program window, in the folder tree, click on the folder.
- On the right side of the window, click right click mouse on Certificates and select All tasks → Import.
- Click "Next .
- Click the Browse button and select the CA.pem file you downloaded earlier. Click Next.
- In chapter Certificate store Leave the default settings and click Next.
- Click Finish.
- (Opt.) In the pop-up dialog, click Agree.
- In the folder tree, click on the folder Trusted Root Certification Authorities→ Certificates.
- In the list of certificates (on the right), find the certificate Certum CA, right-click on it and select Properties.
- Go to the General tab. .
- In the block, set the switch to the Internal position.
- Click OK.
- Try sending a letter. If the certificate error appears again, then in the same block Properties → S/MIME and TLS → Implementing S/MIME and TLS certificates Set the radio button to Microsoft CryptoAPI.
- Click OK button.
Note. The switch positions have to be changed manually, because... in some versions of The Bat! the Internal position will work, in others -
- POP3: server - localhost, port - 110
- IMAP: server - localhost, port - 143
If the problem persists, try using the recommendations from the articles Trade Management Mail Client and gmail (following the recommendations, substitute yandex instead of gmail everywhere) and Sending letters and receiving email using SSL.
I am sending emails from a scanner that does not support SSL
Set up your MFP or scanner as follows:
- Specify the following SMTP parameters:
- server - smtp-devices.yandex.com
- port - 25
- Enable authentication (authentication).
- Enter your username and password in the appropriate fields.
Attention. Be sure to enter your username and password manually. If you select authentication similar to the incoming mail server, sending will not work.
Limitation. You can send letters in this way only to addresses serviced by Yandex.Mail (in the yandex.ru domain or to addresses. To mailboxes of other postal services emails will not be sent through this server.
If you recently changed your mailbox password, make sure you also update your mail program settings. If the password in the settings is correct, wait a few hours - the mail program settings may not synchronize with the Yandex server right away.
Try logging in with the same username and password: enter the authorization data again, rather than using the ones you remembered earlier. If this requires you to enter check digits, you can familiarize yourself with the list possible reasons in the article Why do I need to enter check digits during authorization?
Everyone knows how to work with email. Open the browser and search the right resource, log in and read the incoming email correspondence. The pop3 and imap mail protocols allow you to work with mail without a browser, through client programs, as if the files were located directly on the local computer.
POP3- internet protocol application level, which provides access to the mail server via TCP/IP and using port 110.
IMAP is an application-level Internet protocol that provides access to the mail server via TCP and using port 143.
Difference between POP3 and IMAP
The difference between POP3 and IMAP is application-specific. Both protocols perform identical tasks, only POP3 allows you to download all files at once (correspondence is stored in these files), and IMAP first allows you to download a list of files and then selectively download them yourself. This is the main difference between the protocols, and the newer IMAP was created precisely to implement this difference: clients were not satisfied with the need to parse mail locally, while on the server the files were deleted after downloading. On IMAP servers the user independently manages his messages.
pop3 clients connect to the network only to download files to the local computer, disconnect after the operation is completed, and further program operation takes place in offline mode. IMAP clients can work offline, but online provides more options for them: for example, managing messages on the server. As a result, offline access requires fewer resources and is faster, while online access is more dependent on the network state and demonstrates relatively long time response.
POP3 assumes monouser access to a mailbox, IMAP allows multiple clients to connect to it, while the work of any of them is not limited, and everyone sees the changes made by others. IMAP also allows the user to see the status of messages, move them, create folders and delete them as if he were dealing with a local copy. Automatic removal There are no messages from the server.
Another important difference IMAP from POP3 - in the ability to expand the IMAP protocol and ultimately receive fine tuning, for example, client access rights to the server. Despite the fact that POP3, due to its longevity, is more widespread and easier to configure, IMAP seems more convenient when solving many problems, for example, corporate ones.
TheDifference.ru determined that the difference between IMAP and POP3 is as follows:
IMAP uses port 143, POP3 uses port 110.
IMAP works both online and offline, POP3 works only offline.
IMAP allows you to manage messages directly on the server, POP3 downloads files to the user's local computer.
POP3 provides faster access
In IMAP, you can configure the separation of access rights.
Chances are that most people reading this guide are already familiar with the most commonly used communication technology: email. But have you ever thought about how it actually works? In this article, we will learn how this service works and what POP3, SMTP and IMAP are.
POP3(post office protocol version 3) is often used to communicate with a remote email server and download messages to a local email client and then delete it on the server, for example, Thunderbird, Windows Mail, etc. However, email clients usually offer a choice whether or not to leave copies of messages on the server. If you use multiple devices to send messages, it is recommended to leave this feature enabled, otherwise, on another device you will not have access to sent messages that were not saved on the remote server. It is also worth noting that POP3 is a one-way only protocol, which means that data is taken from a remote server and sent to the local client.
The default POP3 ports are:
Port 110 – port without encryption
Port 995 is an SSL/TLS port, also known as POP3S
Step 2 - Differences between POP3 and IMAP, and what are the ports for IMAP?
IMAP (application layer protocol for accessing email), as well as POP3, is used to receive email messages on a local client, however, it has a significant difference - only the email headers are downloaded, the text of the letter itself remains on the server. This protocol Communication works in two directions; if changes occur on the local client, they are transmitted to the server. IMAP has become more popular recently as giant email service providers like Gmail have started recommending it instead of POP3.
The default IMAP ports are:
- Port 143 – port without encryption
- Port 993 is an SSL/TLS port, also known as IMAPS
Step 3 - SMTP, the protocol for outgoing email communications
Simple Mail Transfer Protocol ( SMTP), is used to communicate with a remote server and then send messages from the local client to the remote server, and ultimately to the message recipient's server. On your email server, this process is controlled by a special service ( MTA). It's worth mentioning that SMTP is used solely for sending messages.
SMTP Ports:
- Port 25 – port without encryption
- Port 465 is an SSL/TLS port, also known as SMTPS
Conclusion
We hope that you now have a clear understanding of how email protocols work and what ports they use. In this tutorial, we learned what POP3, SMTP and IMAP are and what they are used for. For example, POP3 and IMAP are used for the same purposes, but they approach these tasks differently. IMAP leaves the content of the message on the server, and POP3 downloads it to your computer. Also, we found out what the standard ports are for SMTP, POP3 and IMAP.
There are two main methods of working with mail: Online and Offline.
According to the offline method, mail is delivered to the server, and the PC user periodically launches an email client, which downloads all new mail on PC. All mail processing, such as filtering, takes place on local machine. Offline access? a “store and forward” service designed to forward mail on demand from a mail server to a single endpoint machine. Once delivered to the destination machine, the messages are deleted from the mail server.
In the case of online access, mail is also delivered to the shared server, but the client no longer copies all mail and then deletes it from the server. The online approach is more client-server. In this case, the client can ask the server for the header of the message or request that the message be searched by some criterion. Messages can be marked with various status flags (for example, the message has been marked for deletion or a reply has been sent to it) and these marks are retained until they are explicitly deleted by the user (which may not happen until the next session).
- Advantages of the offline method:
- Minimum time connections to the server.
- Minimal use of server resources.
- Advantages of the online method:
- Ability to use different computers at different times.
- Ability to use?lightweight? client machines.
- Platform-independent access to multiple mailboxes.
- Possibility of simultaneous access to shared mailboxes.
The main advantage of online access is that mailboxes with incoming and archive mail are stored on the server and can be accessed uniformly from various computers at different times. And all this can be done without using file sharing protocols (these protocols do not exist on every platform, can be inferior in performance and cause file locking problems). All this is not necessary for those users who always use the same same computer for accessing mail, but becomes very important for those who use multiple computers.
Opportunities and
POP was designed to support offline mail processing. And although offline access restrictions can be compensated by using this protocol in online mode POP simply does not have some of the functionality required for high-quality online access. The pseudo-online access mode supported by POP3 is that the user leaves mail on the server and this often requires a remote file system protocol so that the mail client can update the mailbox or set message flags. IMAP can also be used for offline access, but its power manifests itself primarily with online access. In a nutshell, IMAP allows you to manipulate remote mailboxes as if they were local. Depending on the implementation of the IMAP client and the mail architecture that the manager wishes to have postal system, the user can save messages only on the client machine, only on the server, or have the choice to do both.
Let us now present quick comparison POP3 and IMAP4 protocols.
- Characteristics common to both protocols
- Both support offline access
- Mail is delivered to a shared, always-on mail server
- New mail is accessible from more client platforms and from anywhere on the web
- The protocols are open and standardized (there are corresponding RFCs on the Internet)
- Focused only on reading mail, both use
- Both protocols support persistent message IDs (POP3 - not all servers) which are used for disconnected access
- Benefits of POP3
- Easier to implement
- More clients exist at the moment
- Benefits of IMAP4
- Can manipulate persistent message flags (Seen, Draft, Deleted,?).
- It can both store messages and download them. It is possible to add messages to your mailbox.
- Can work with multiple mailboxes (possibly even hierarchical ones).
- Can support parallel access to mailboxes and parallel updating of mailboxes.
- Suitable for accessing non-mail data, such as news or documents.
- Can use offline access to reduce connection time and used disk space.
- Allows you to search for messages on the server.
- It is possible to download part of a letter, and you can download a fragment starting from any place and of any length.
- Designed specifically to improve online access performance, especially for slow connections.
- IMAP4 rev 1 supports Unicode standard(mailboxes with Unicode names, message search)
- There is a standardized way to extend basic protocol. In particular, there are extensions for managing user quotas and their access rights to other people's or shared mailboxes.
- Are there ?companion protocols? (IMSP and its ACAP receiver) to store and manipulate user settings.
More about IMAP4
IMAP can manipulate persistent message status flags, including ?Seen?, ?Deleted?, ?Answered?, as well as user-defined flags. IMAP allows you to store messages and also receive them from the server. A user can add a message from an inbox to an archive box (or vice versa). Using IMAP, a client can access and manage multiple mailboxes. This includes both the ability to name and access various archive and inboxes, as well as the ability to list, create, delete, and rename them. These mailboxes can be located on the same or on different mail servers. An IMAP client can allow you to see them all at once and move messages from one mailbox to another.
IMAP can allow simultaneous access and updating of shared mailboxes. This ability is convenient if several clients process messages arriving in a common inbox. All active clients are notified of mailbox state changes via IMAP.
IMAP can be used to access non-mail data, such as Newsgroups. This is convenient from the point of view of unifying the method of access to various classes of information. IMAP also supports offline access, which saves connection time to the server and server resources. The offline method is convenient to use in situations where access to the server occurs only over an expensive dial-up connection and multi-platform access to any mailbox is not required. It is also beneficial to use such access if the client machine is rich in resources and the server is poor.
Not all IMAP clients offer support for offline mode, but the protocol allows this to the fullest. IMAP has a companion protocol for managing user settings called IMSP, Internet Message Support Protocol. IMSP enables location-independent (multi-platform) access to the user's personal settings, e.g. address book. (Its descendant ACAP also allows you to store settings for servers and user groups. ACAP is specially optimized to reduce the amount of data sent over the network, has rich search capabilities on the server side, and allows you to manage data access rights.)
IMAP has designs to optimize online access, especially over low-speed links. These designs include the ability to get the structure of a message without downloading it entirely to client machine, selective downloading of parts of a message and the ability to use the server for searching, in order to reduce the amount of data transferred between the client and server. It can be very useful to delay sending some messages or parts of them (from the server to the client machine) until the appropriate moment, if the messages are not of immediate interest. If the message contains attached documents or multimedia data, transmitting only part of the message can be a big advantage. This can be felt quite clearly, for example, if you are in a hotel and they send you short message with attached 10 MB video clip.
Efficient handling of MIME messages is a significant advantage of IMAP over POP. (MIME stands for Multipurpose Internet Mail Extensions, a standard for encoding messages containing arbitrary file attachments. Once MIME messages are encoded, they can be sent using SMTP.) To summarize, we can say that
IMAP beats POP in three areas:
- richer functionality for mailbox manipulation;
- the ability to manage several mailboxes rather than just one;
- primitives for optimizing online access performance, especially when it comes to large MIME messages.
Advantages of POP over IMAP:
- the presence of a larger number of implementations, both clients and servers;
- ease of setup (since POP has little functionality, you don’t need to configure anything).
In my opinion, over time, IMAP should supplant POP. A description of POP3 can be found in RFC-1939. IMAP4 is described in RFC-2060.
IMAP list software can be found at /go?www.imap.org/products.html, and a list of IMAP-related documents can be found at /go?www.imap.org/biblio.html.
Also of potential interest may be /go?www.imap.org/imap.docs.html (a collection of IMAP documents); Message Access Paradigms and Protocols ( this document is more full description ideas presented in the article, in addition, it describes in detail the terminology and provides information about POP protocols and IMAP in the context of online access).