I have Zentyal/postfix configured to send mail through a smarthost at a larger provider, and grab it through the same using fetchmail since many spam heuristics are suspicious towards smaller, independent mail servers.
Problem is as follows: I want to force use of the smarthost independent of which destination outgoing mail has. Even if it is a destination domain name that the mail server is set to handle, I still want it to go through the smarthost.
Is there any good way to do this? I tried commenting out virtual_mailbox_domains in main.cf.mas and rebuilding and restarting the server. This makes one able to send mail to "nonexistent" users on the Zentyal server (which do not exist there but only at the bigger mail provider), but since Fetchmail passes mail to Postfix, there is no longer any destination for the incoming mail Fetchmail grabs for a user so it just disappears. (Off-topic but this also makes me a bit worried, does that mean mail will start flushing out into thin air if the Postfix module stops working?)
Also tried setting transport_maps in main.cf.mas to point to a file containing * smarthost:port and then running sudo postmap that_file. Rebuild and restart. No change stuff addressed to the domain still bypasses smarthost.
Any tips much appreciated
Thanks in advance