Hi there all, I seem to have some issues with my mail (SPF related I think). Basically my setup is this. I have 4 servers running. DNS Server Mail Server Webserver #1 Webserver #2 Now, the main mail server is running perfectly fine using a slightly customised variant of the 'Virtual Users With MySQL Postfix' setup. The issue I'm having (which isn't really related to that mail server) is that on the webservers, some people using the PHP mail function aren't having their messages delivered. The server is trying to deliver them via sendmail. From what I gather it may have something to do with reverse lookups, but I'm not sure. Is it fine to have sendmail running standalone on the server, or do I need to install Postfix on the webservers as well? My mail log file looks like this.. Code: Feb 9 13:42:37 webforma sendmail: p19Dgamu027691: from=webforma, size=186, class=0, nrcpts=1, msgid=<201102091342.p19Dgamu027691@webforma.core01.zen-studios.com>, relay=webforma@localhost Feb 9 13:42:37 webforma sm-mta: p19Dgbfd027692: from=<email@example.com>, size=439, class=0, nrcpts=1, msgid=<201102091342.p19Dgamu027691@webforma.core01.zen-studios.com>, proto=ESMTP, daemon=MTA-v4, relay=localhost.localdomain [127.0.0.1] Feb 9 13:42:37 webforma sendmail: p19Dgamu027691: firstname.lastname@example.org, ctladdr=webforma (1001/1001), delay=00:00:01, xdelay=00:00:00, mailer=relay, pri=30186, relay=[127.0.0.1] [127.0.0.1], dsn=2.0.0, stat=Sent (p19Dgbfd027692 Message accepted for delivery) Feb 9 13:42:39 webforma sm-mta: p19Dgbfd027692: to=<email@example.com>, ctladdr=<firstname.lastname@example.org> (1001/1001), delay=00:00:02, xdelay=00:00:02, mailer=esmtp, pri=120439, relay=mailserver.webforma.co.uk. [22.214.171.124], dsn=5.1.1, stat=User unknown Feb 9 13:42:39 webforma sm-mta: p19Dgbfd027692: p19Dgdfd027694: DSN: User unknown Feb 9 13:42:39 webforma sm-mta: p19Dgdfd027694: to=<email@example.com>, delay=00:00:00, xdelay=00:00:00, mailer=local, pri=30000, dsn=2.0.0, stat=Sent I'm not too sure what the DSN errors mean, or why it's saying user unknown. Any help on this matter would be greatly appreciated. Edit: Just to clarify, the webserver in question is 'webforma.core01.....', and it's obviously delivering to mailserver.webforma.co.uk. I could see how it might be confusing.