The POP3 port ( post office protocol ) is the standard Internet protocol for the application layer, which is used by local e-mail clients to retrieve data from a remote server via a TCP / IP connection.
POP3 is used to communicate with a remote mail server and download email to a local mail client. If you access the same account from different devices, it is recommended that you keep deleted copies, as otherwise your second device will not download emails if the first one has already deleted them. It is also worth mentioning that POP3 is a one-way communication protocol, which means that data is retrieved from a remote server and sent to a local client.
POP3 port: technology overview
The POP protocol supports load and delete requirements for accessing remote mailboxes (called maildrop in POP RFC). Although most clients have the ability to leave mail on the server after downloading, email applications that use POP usually connect, receive all messages, save them to the user's PC as new messages, delete them from the server, and then disconnect them.
Other protocols, such as IMAP (Internet Message Access Protocol), provide more comprehensive and complex remote access to typical mailbox operations. In the late 1990s and early 2000s, fewer Internet service providers supported IMAP because of the storage space that was required on the service provider's hardware.
Modern e-mail clients support POP. Over time, popular email software has added IMAP support.
Technical features
The server works with well-known port 110. POP3 SSL port is the latest standard for general use. Encrypted communication for the protocol is requested using the STLS or POP3S command, which connects to the server using the Transport Layer Security (TLS) or Secure Sockets Layer (SSL).
Available messages to the client are recorded when the POP3 port server opens the mailbox and is verified by the message number, which is the local identifier for the message that is local to this session. This parameter is permanent and unique to maildrop and allows the client to access the same message in different sessions. Mail is retrieved and marked for deletion by message number. When a client leaves the session, mail marked for deletion is deleted from maildrop.
History and documentation
The first version (POP1) was specified in RFC 918 (1984), POP2 according to RFC 937 (1985). POP3 was initiated by RFC 1081 (1988). Its current RFC 1939 specification has been updated with the RFC 2449 extension mechanism and the authentication mechanism in RFC 1734.
POP3 currently supports several authentication methods to provide various levels of protection against illegal user email access. Most of them are provided by POP3 expansion mechanisms. Clients support SASL authentication methods through the AUTH extension. The MIT Athena project has also released a version of Kerberized. RFC 1460 introduced APOP in its core protocol. APOP is a call / response protocol that uses the MD5 hash function to avoid retries and privacy breaches.
POP4 exists only as an unofficial offer that adds basic folder management, multiple message support, and message flag management to compete with IMAP. The POP4 version has not been developed since 2003.
Extensions and Specifications
The mechanism was proposed in RFC 2449 to host common extensions, as well as organized support for additional teams such as TOP and UIDL. The RFC does not intend to encourage extensions, and reaffirmed that the role of POP3 is to provide simple support, mainly for loading and removing mailbox processing requirements.
Extensions in official documentation are called features and are listed by the CAPA team. With the exception of APOP, optional commands were included in the initial feature set.
STARTTLS and SDPS Extensions
This extension allows you to use the Transport Layer Security protocol or Secure Sockets Layer protocol using the STLS command on the standard POP3 port, and not on the alternative one. Some clients and servers use the alternative port method, which uses TCP port 995 (POP3S).
Demon Internet introduced the extension for POP3, which allows you to attach multiple accounts to the same domain, and became known as the standard POP3 dial-up service (SDPS). To access each account, the login includes the host name, like john @ hostname or john + hostname.
Kerberized Post Office Protocol
In the calculation, local email clients can use the Kerberized Post Office Protocol (KPOP) Internet Protocol to receive email from a remote server over a TCP / IP connection. The KPOP protocol is based on the POP3 protocol with the difference that it adds Kerberos security and works by default on the TCP port number 1109 instead of 110. One version of the mail server software is located on the Cyrus IMAP server.
Comparison with IMAP
POP3 SSL port is a much simpler protocol that simplifies implementation. Mail moves the message from the email server to your local computer, although it is usually possible to leave messages on the email server.
IMAP, by default, leaves a message on the email server, simply downloading a local copy.
POP treats a mailbox as one store, and has no idea about folders.
The IMAP client makes complex queries, queries the server for the headers or content of certain messages, or searches for emails matching certain criteria. Messages in the mail repository can be marked with various status flags (for example, “deleted” or “replies”), and they remain in the repository until the user explicitly deletes them.
IMAP is designed to manage remote mailboxes as if they were local. Depending on the IMAP client implementation and the mail architecture required by the system manager, the user can save messages directly on the client machine or save them on the server, or they are given a choice.
POP requires that the client currently connected is the only client connected to the mailbox. In contrast, IMAP allows multiple clients to access simultaneously and provides mechanisms for detecting changes made to the mailbox by other clients that are simultaneously connected.
When POP receives a message, it receives all its parts, while IMAP4 allows clients to extract any of the MIME parts separately - for example, to receive plain text without receiving attachments.
IMAP supports flags on the server to track the status of a message: for example, whether a message has been read, a response is provided, or a message is deleted.
What are POP and IMAP and which one should be used for email?
If you have ever set up an email client or application, you probably came across the terms of the POP3, SMTP, and IMAP ports. Do you remember which one you chose and why? If you are not completely sure what these terms mean and how each affects your email account, the information below will shed some light on this issue. This article explains how POP and IMAP work and helps you decide which one best suits your needs.
Both email protocols allow you to read emails locally using a third-party application. Examples are Outlook, Thunderbird, Eudora, GNUMail, or (Mac) Mail.
The original protocol is POP. It was created in 1984 as a tool for downloading emails from a remote server. IMAP was developed in 1986 to provide remote access to emails stored on a remote server. In fact, the main difference between the two protocols is that POP downloads emails from the server for permanent local storage, while IMAP leaves them on the server and simply caches (temporarily) stores messages locally. In other words, IMAP is a form of cloud storage.
Distinctive features of POP and IMAP?
These two protocols are best compared by looking at their basic workflows.
POP workflow:
- connection to the server;
- receiving mail;
- local data storage;
- removal of correspondence from the server;
- shutdown.
The default POP behavior is to delete mail from the server. However, most clients also provide the option to leave a copy of the downloaded mail on the server.
The default POP3 ports are:
- port 110 - unencrypted port;
- port 995 - SSL / TLS port, also known as POP3S.
IMAP workflow:
- connection to the server;
- extraction of the content requested by the user and local caching (list of new letters, summary of messages or contents of selected letters);
- processing of user changes, for example, marking read letters, deleting data;
- shutdown.
As you can see, the IMAP workflow is a bit more complicated than POP. In essence, folder structures and emails are stored on the server, and only copies are stored locally. Typically, these local copies are stored temporarily. Nevertheless, storage of them on an ongoing basis is available.
By default, IMAP ports are:
- port 143 - unencrypted port;
- port 993 - SSL / TLS port, also known as IMAPS.
What are the benefits of POP?
Being the original protocol, POP follows the simplified idea that only one client requires access to mail on the server and that emails are best stored locally. This leads to the following benefits:
- mail is stored locally, i.e. always available, even without an internet connection;
- An Internet connection is only necessary for sending and receiving mail;
- saves space on the server;
- the ability to leave a copy of mail on the server.
- Consolidate multiple email accounts and servers into one mailbox.
What are the benefits of IMAP?
As mentioned in the introduction, IMAP was created to provide remote access to emails stored on a remote server. The idea was to allow multiple clients or users to manage the same mailbox. Thus, regardless of the device through which you log in to your account, you will always see the same email and folder structures, as they are stored on the server, and all changes you make to local copies are immediately synchronized with the server.
As a result, IMAP has the following advantages:
- mail stored on a remote server is accessible from several places;
- To access mail you need an Internet connection;
- Faster browsing because only headers are downloaded until the content is explicitly requested
- mail is automatically reserved if the server is properly managed;
- local storage space is saved;
- the ability to store mail locally.
Which email protocol is the best?
The choice of protocol depends on your specific needs and current work situation. The following points should help make a final decision.
Choose POP if:
- You want to access your mail from only one device.
- You need constant access to your email, regardless of Internet access.
- You have limited storage on the server.
Select IMAP if:
- You want to access your email from multiple devices.
- You have a reliable and permanent internet connection.
- You want a brief overview of new letters or letters on the server.
- Your local storage is limited.
- You are worried about supporting your emails.
If in doubt, contact IMAP. This is a more modern protocol that allows you to be flexible, and your email is automatically backed up on the server. In addition, server space is usually not a problem these days, and you can still store important emails locally.
Email client errors
If you encounter a POP3 error, port: 995, Secure (SSL) with the number 0x800C0133 when trying to check your Gmail, then try to compress your mail folders. In the POP client, select File> Folder> Compress All Folders. This should fix the problem.