Email protocols

There are 3 main email protocols used : POP3 and IMAP for mail retrieving and SMTP for sending emails.

Acronyms :
POP (Post Office Protocol)
IMAP (Internet Message access protocol)
SMTP (Simple mail transfer protocol)

POP3 downloads the emails from the server (and if not specified to keep a copy it also deletes the emails) - you have to make rules to filter the email on every client individually and if you lose the email client database you lose all your filters and emails.
Pop3 is good if you have a low email quota and you like your privacy (because as soon as an email is read is deleted from the server) 

IMAP synchronizes you folders and email from the server to you mail client and does not delete the messages unless you delete them.
Main advantage to imap is the it syncs your emails,folders etc the same way on any device.

POP3 : 110 and secure POP3 with SSL/TSL 995
IMAP : 143 and secure IMAP with SSL/TSL 993
SMTP : 25 and secure SMTL with SSL/TSL 465 

SMTP port is 25 and is usually blocked by the ISP to prevent spam by infected users.