POP3 Port (Post Office Protocol) is a standard Internet application layer protocol used by local e-mail clients to retrieve data from a remote server over a TCP/IP connection.
POP3 is used to connect to a remote mail server and download email to a local mail client. If you're accessing the same account from multiple devices, it's a good idea to keep deleted copies, as otherwise your second device won't download emails if the first one has already deleted them. It's also worth mentioning that POP3 is a one-way communication protocol, which means data is retrieved from a remote server and sent to a local client.
POP3 port technology overview
The POP protocol supports download and delete requirements for accessing remote mailboxes (called maildrop in the POP RFC). Although most clients have the ability to leave mail on the server after download, email applications using POP usuallyconnect, receive all messages, save them to the user's PC as new messages, delete them from the server, and then disconnect.
Other protocols such as IMAP (Internet Message Access Protocol) provide more complete and sophisticated remote access to common mailbox operations. In the late 1990s and early 2000s, fewer ISPs supported IMAP due to the storage space required on the ISP's hardware.
Modern e-mail clients support POP. Over time, popular email software added support for IMAP.
Specifications
The server is running on the known port 110. The POP3 SSL port is the latest standard in common use. Encrypted communication for the protocol is requested using the STLS or POP3S command, which connects to the server using Transport Layer Security (TLS) or Secure Sockets Layer (SSL).
Available messages to the client are captured when the POP3 port server opens the mailbox and is verified against the message number by the session-local unique identifier assigned to the message. This setting is persistent 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 logs out of a session, mail marked for deletion is removed from the maildrop.
History and documentation
Firstversion (POP1) was specified in RFC 918 (1984), POP2 in 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 multiple authentication methods to provide different levels of protection against illegal access to a user's email. Most of these are provided by the POP3 extension 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 to the core protocol. APOP is a challenge/response protocol that uses the MD5 hash function to avoid retries and privacy violations.
POP4 only exists as an unofficial proposal adding basic folder management, support for multiple messages, and message flag management to compete with IMAP. The POP4 version has not been developed since 2003.
Extensions and Specifications
A mechanism was proposed in RFC 2449 to accommodate common extensions as well as organized support for additional commands such as TOP and UIDL. The RFC does not intend to encourage extensions and has confirmed that the role of POP3 is to provide simple support mainly for downloading and removing mailbox processing requirements.
Extensions are called features in the official documentation and are listed by the CAPA team. Except APOP, optionalcommands have been included in the initial feature set.
STARTTLS and SDPS extensions
This extension allows you to use the Transport Layer Security or Secure Sockets Layer protocol using the STLS command on a standard POP3 port, not an alternative one. Some clients and servers use the alternate port method, which uses TCP port 995 (POP3S).
Demon Internet introduced an extension to POP3 that allowed multiple accounts to be attached to the same domain, and became known as the Standard POP3 Dial-Up Service (SDPS). To access each account, the login includes a hostname, like john @ hostname or john + hostname.
Kerberized Post Office protocol
When computing, 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 differences that it adds Kerberos security and runs on TCP port number 1109 instead of 110 by default. One version of the mail server software resides on the Cyrus IMAP server.
Comparison with IMAP
POP3 The 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 by simply downloadinglocal copy.
POP treats the mailbox as a single store and has no concept of folders.
An IMAP client performs complex queries, queries the server for the headers or content of certain messages, or searches for messages that match certain criteria. Messages in the mail repository can be marked with various status flags (such as "deleted" or "replies") and 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 implementation of the IMAP client and the mail architecture required by the system manager, the user may store messages directly on the client machine, or store them on the server, or they are given a choice.
The POP protocol requires that the currently connected client be the only client connected to the mailbox. In contrast, IMAP allows simultaneous access by multiple clients and provides mechanisms for detecting changes made to a mailbox by other simultaneously connected clients.
When POP receives a message, it gets all of its parts, whereas IMAP4 allows clients to extract any of the MIME parts separately - for example, to get plain text without getting attachments.
IMAP maintains flags on the server to keep track of the status of a message, such as whether the message was read, answered, or deleted.
What are POP and IMAP and which one should I use for email?
If you've ever set up an email client or application, you've probably come across POP3, SMTP, and IMAP port conditions. Do you remember which one you chose and why? If you're not quite sure what these terms mean and how each affects your email account, then the information below will shed some light on the matter. This article explains how POP and IMAP work and will help 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 means to download emails from a remote server. IMAP was developed in 1986 to provide remote access to emails stored on a remote server. Essentially, 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) the emails locally. In other words, IMAP is a form of cloud storage.
Differences between POP and IMAP?
These two protocols are best compared by looking at their core workflows.
POP Workflow:
- connectionto the server;
- receiving mail;
- local data storage;
- deleting correspondence from the server;
- off.
POP's default behavior is to delete mail from the server. However, most clients also provide the option to leave a copy of downloaded mail on the server.
Default POP3 ports:
- port 110 - unencrypted port;
- port 995 - SSL / TLS port, also known as POP3S.
IMAP workflow:
- connect to server;
- retrieve user-requested content and cache locally (list of new emails, summaries of messages, or content of selected emails);
- handling user changes, such as marking emails as read, deleting data;
- off.
As you can see, the IMAP workflow is a bit more complicated than POP. Essentially, folder structures and emails are stored on the server, and only copies are kept locally. Typically, these local copies are stored temporarily. However, permanent storage is available.
Default IMAP ports:
- 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 simplistic idea that only one client needs to access mail on the server and that mail is best stored locally. This results in the following benefits:
- mail is stored locally, i.e. always available, even without connection toInternet;
- Internet connection is only required to send and receive mail;
- saves space on the server;
- the ability to leave a copy of the 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. This way, no matter which device you use to log into your account, you will always see the same email and folder structures as they are stored on the server, and any changes you make to your local copies are immediately synced to the server.
As a result, IMAP has the following advantages:
- mail stored on a remote server is accessible from multiple locations;
- Internet connection required to access mail;
- faster browsing as only headers are loaded until content is explicitly requested;
- mail is automatically reserved if the server is properly managed;
- preserves local storage space;
- the ability to store mail locally.
Which email protocol is the best?
The choice of protocol depends on your specific needs and current working situation. The following points should help you make the final decision.solution.
Select POP if:
- You only want to access your mail from one device.
- You need constant access to your email, regardless of Internet availability.
- You have limited server storage.
Select IMAP if:
- You want to access your email from multiple devices.
- You have a reliable and constant Internet connection.
- You want to get a quick overview of new emails or emails on the server.
- Your local storage is limited.
- You are worried about maintaining your emails.
If in doubt, please contact IMAP. This is a more modern protocol that allows you to be flexible and your email is automatically backed up on the server. Plus, server space isn't usually an issue these days, and you'll still be able to store important emails locally.
Mail client errors
If you encounter a POP3, port: 995, Secure (SSL) error number 0x800C0133 when trying to check your Gmail, try compressing your mail folders. In the POP client, select "File" > "Folder" > "Compress all folders". This should fix the issue.
