POP3(邮局协议 3)和 IMAP(Internet 消息访问协议)都是 MAA(消息访问代理)，这两个协议都用于从邮件服务器到接收方系统检索消息。这两种协议都考虑了垃圾邮件和病毒过滤器。 IMAP 比 POP3 更加灵活和复杂。
POP3 和 IMAP 的区别：
| Post Office Protocol (POP3) | Internet Message Access Protocol (IMAP) |
|---|---|
| POP is a simple protocol that only allows downloading messages from your Inbox to your local computer. | IMAP is much more advanced and allows you the user to see all the folders on the mail server. |
| The POP server listens on port 110, and the POP with SSL secure(POP3DS) server listens on port 995 | he IMAP server listens on port 143, and the IMAP with SSL secure(IMAPDS) server listens on port 993. |
| In POP3 the mail can only be accessed from a single device at a time. | Messages can be accessed across multiple devices |
| To read the mail it has to be downloaded on the local system. | The mail content can be read partially before downloading. |
| The user can not organize mails in the mailbox of the mail server. | The user can organize the emails directly on the mail server. |
| The user can not create, delete or rename email on the mail server. | The user can create, delete or rename email on the mail server. |
| A user can not search the content of mail before downloading to the local system. | A user can search the content of mail for specific string before downloading. |
|
It has two modes : delete mode and keep mode. In delete mode , the mail is deleted from mail box after retrieval. In keep mode , the mail remains in the mail box after retrieval. |
Multiple redundant copies of the message are kept at the mail server, in case of loss of message of a local server, the mail can still be retrieved |
| Changes in the mail can be done using local email software. | Changes made web interface or email software stay in sync with the server. |
| All the message are downloaded at once. | Message header can be viewed prior to downloading. |