Email & Messaging

TCP 25 carries SMTP mail transfer, commonly between mail servers. Mail clients should use the submission endpoint specified by their provider.

Post Office Protocol version 2 (POP2)

POP3 (Post Office Protocol 3) for receiving email

IMAP on TCP 143 can upgrade a connection with STARTTLS when supported. It differs from implicit TLS on port 993.

Port 465 is used for mail submission with implicit TLS: the TLS handshake begins immediately after the TCP connection.

Port 587 is for message submission, commonly from a mail client to its provider. Distinguish it from server-to-server relay on port 25.

Port 993 provides IMAP mailbox access over implicit TLS. It is for reading and synchronizing mail, not SMTP submission.

POP3S (POP3 over SSL/TLS) Security POP3Protocolport