IMAP and POP servers
Email can be retrieved from a server either through a shared file
system or IMAP or POP3 servers.
POP servers allow to retrieve e-mail with its headers, delete it on the server or leave
a copy in the original Inbox or directory. It listents on port tcp/110.
Besides the POP functionalities, IMAP allows to read only e-mail headers,
create new folders and move e-mail to the folders. IMAP listens on port tcp/143.
Use POP if you don't need to store e-mail on the server and use IMAP
otherwise.
Both IMAP and POP require user authentication to access email.
Popular IMAP and POP servers
UW IMAP and POP. Uses Inbox (mbox) format.
Cyrus IMAP and POP. Uses Inbox format for incoming mail and its own mailbox
format for folders.
Courier IMAP and POP3. Use Maildir format.
Dovecot IMAP and POP3. Uses both Inbox and Maildir formats.