Port 143 supports IMAP and Internet Message Access Protocol (UDP reference coverage) across distinct transports. Review each protocol before writing firewall or monitoring policy.
Mailbox access using IMAP, optionally upgraded with STARTTLS.
Mail clients synchronizing server-hosted folders and messages.
Client to server
Require STARTTLS and strong authentication, or prefer implicit TLS on 993.
Internet Message Access Protocol (UDP reference coverage) is documented as a network service convention for port 143 over UDP.
Use this reference entry when identifying or validating systems documented to use 143/UDP.
Varies
Confirm the listening process and current vendor documentation before permitting traffic; a listed convention does not prove the active service or its security posture.