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