Some mail servers can be configured to receive incoming SMTP mail on a non-standard port. The CommuniGate Pro SMTP module can send messages to those servers, if the domain part of an E-mail address contains the port number or is routed to an address that includes the port number.
Use the ._relay or ._via suffix with the port number: domain.port._relay. The SMTP module will not use the domain MX records in this case, it will try to resolve the domain name directly into an IP address. Sample Router record: secret.communigate.com = mail.communigate.com.26._relay