On Mon, 2011-08-22 at 13:07 +0100, Anne Wilson wrote:
anne@xxxx.org: host mailhost.zen.co.uk[212.23.3.98] said: 550-Verification failed for anne@xxx.lan 550-Unrouteable address 550 Envelope Sender: Domain must resolve in DNS! (in reply to RCPT TO command)
Once your email is out on the Internet is needs a genuine Internet email address. xxx.lan is known only to your internal system and it is not an Internet email address.
Care to show the headers of your outgoing email ? (cover-up the bits you want to keep private)