SMTP
Server to server mail transfer
Security: Require STARTTLS; never operate an open relay
TCP · Encrypted: Optional
Port
Port 25
Conventionally used by SMTP. Port assignments are conventions, so confirm the actual listener before you write a rule around this number.
TCPEncrypted: Optional
Protocols on this port
Where this port appears in the documentation
Exposure guidance
Decide reachability from the identity of the caller, not from the port number. If the service on this port carries credentials or administrative control, restrict it to an administrative network, require strong authentication, and log every session that reaches it.
Nearby ports
In the knowledge graph
Open the interactive map centred on this entity to see everything it connects to and travel outwards from there.