Network ports used in conjunction with IP addresses are used to define the TCPIP socket for network connections between hosts on an (inter)network so they can communicate with each other. Some port numbers are classics and here are those used for electronic mail.

POP3 – port 110

IMAP – port 143

SMTP – port 25

HTTP – port 80

Secure SMTP (SSMTP) – port 465

Secure IMAP (IMAP4-SSL) – port 585

IMAP4 over SSL (IMAPS) – port 993

Secure POP3 (SSL-POP) – port 995