IMAP (an application-layer protocol for email access), just like POP3, is used to retrieve email messages to a local client; however, it has a significant difference: only the email headers are downloaded, while the message body itself remains on the server. This communication protocol works two-way; if changes occur on the local client, they are also transmitted to the server. Recently, IMAP has become more popular as major email service providers like Gmail have started recommending its use instead of POP3.
Default IMAP ports are:
- Port 143 is an unencrypted port
- Port 993 is an SSL/TLS port, also known as IMAPS