SMTP Email Problems

I cannot open SMTP sessions (ie: send mail)?

This is a somewhat rare issue that only arises when clients are running their own mail server. This example uses a Postfix MTA, add the following line to the master.cf
465          inet     n             –             n             –             –             smtpd
The port (465) will have to match the client software and may need to be something else, eg: the more usual port 25.