Does your postfix send emails directly or do you use a smarthost for relaying? I'm asking because you're using a 10.x.y.z network which means you use NAT for outgoing connections when delivering mails directly to the destination server. Bad idea. Worse if the destination server does some sanity checks (like spf or reverse checking of your ip/dns etc). Brgds -- Freundliche Gruesse/Best Regards Benjamin Hackl IT/Administration Media FOCUS Research Ges.m.b.H. Maculangasse 8, 1220 Wien Austria Tel: +43 1 258 97 01-295 b.hackl at focusmr.com