Postfix Admin

In postfixadmin's default config, a valid mail address needs to contain a valid domain part which is resolvable by your nameserver. "admin@server.local" won't work, "admin@sourceforge.net" (or @aonther existing domain) should work.

If you see the error message while using a valid domain name, check if your nameserver (see /etc/resolv.conf) can resolv the domain correctly.

If everything failes, set $CONF['emailcheckresolvedomain']='NO' - but be warned that postfix etc. depend on a working nameserver...