Hello,
I run a small publishing company and for the sake of easing communication between authors (who work in teams) I have provided each of them with a local alias. Typically, mail sent to <firstname>.<lastname>@<mydomain> is redirected to <firstname>.<lastname>@gmail.com, the usual email address of the author.
I've been using this for 15+ years and it's been great. Unfortunately, I'm losing the war against spam. In spite of careful configuration of Postfix, the use of Postgrey and hand-drawn blacklists, too much spam passes through. What my server regards as legitimate email (but is sometimes spam) gets resent to sites such as GMail which, in turn, tend to flag all email from my domain as spam, even legitimate emails. And this is starting to jeopardize my communication with the rest of the world.
In this very special setting, I have a solution that preserves functionality: all email adressed to me (through various aliases) should come to my box with only the usual filters enabled, but an email for an author (@<mydomain>) should be allowed to pass through only if it is sent from the usual email address of another author. I have a complete list of all these valid sender email addresses (most authors use several). For instance, if authors Alice and Bob have email addresses al...@gmail.com and b...@gmail.com, Alice can write to bob@<mydomain> from her GMail account. But emails sent to bob@<mydomain> from an address unknown in my database should be silently dropped.
I have turned to Postfix' documentation to find the best way to do this. I thought that among the seemingly endless options for main.cf one would match, but I could not find it. Perhaps I didn't understand enough to identify the right one. The difficulty seems to be that the rule for authors must not apply to me, because I need to be contacted by people whose email address I don't already know.
I also looked Postfix' documentation about milters. These really look like what I need to put in place, if a simpler solution cannot be found. I can write a nice program in Perl. But hooking a Perl script into Postfix as a milter seems quite specific and the documentation is rather evasive on this matter.
Which way of configuring Postfix would you recommend for this job? Thanks for you help ! Sébastien.
