Post Office Protocol version 3 (POP3) is a standard protocol used by email clients to retrieve email that has been delivered to and stored on an email server.

POP3 communications typically occur on TCP port number 110.

Unlike IMAP, after a POP3 client downloads an email to the email user’s computer, a copy of the email usually does not remain on the email server’s hard disk. The advantage of this is that it frees hard disk space on the server. The disadvantage of this is that downloaded email usually resides on only one personal computer. Unless all of their POP3 clients are always configured to leave copies of email on the server, email users who use multiple computers to view email, such as both a desktop and laptop, will not be able to view from one computer any of the email previously downloaded to another computer.

FortiMail units do not scan POP3 traffic for spam and viruses, but may use POP3 when operating in server mode, when an email user retrieves their email.