There are 65 535 ports available for each of the TCP and UDP stacks that applications can use when communicating with each other. If someone recently changed a FortiMail or network port, that may be part of your problem.

In addition, some ports may be assigned to other Fortinet appliances on your network. See the Fortinet Knowledge Base article, "Traffic Types and TCP/UDP Ports used by Fortinet Products" at:

Many UDP and TCP port numbers have internationally recognized ANA port assignments and are commonly associated with specific applications or protocols.