I am used to sendmail and am using Postfix now and am uncertain of some features. I typically would comment out the line in sendmail.mc that went something like 'accept unresolvable domains'
I tried using
smtpd_sender_restrictions = reject_unverified_sender reject_unverified_smtp
and this seems a bit too restrictive and got some bounces on legitimate senders
so I'm thinking that this is perhaps a bit more apropos...
smtpd_helo_restrictions = permit_mynetworks, reject_invalid_hostname
does this make sense?
Craig