Any Postfix gurus here?
Some time ago I set up Postfix based on a collection of How-To's and it works but I don't sufficiently understand the configuration to make changes safely.
At the moment it received email on port 25 for a number of domains (specified in a MySQL database); it sends them via a dspam content_filter which redelivers on port 10026 from which the majority of email is dropped into MailDir mailboxes for Dovecot to make available via POP3, although some mail is forwarded to other addresses (eg gmail accounts). All of that is working.
What I want to add is that for some domains, after spam checking they get forwarded to another SMTP server (specified in the database per-domain). Those servers will typically be Exchange servers within people's offices.
I'm not sure what info I can offer to enable someone to help me, as I'm sure the above is nowhere near enough.
I'm running on an Ubuntu server using standard repo packages only.