Hi Luvers, Here is scenario (not for me by the way, but someone else) Using laptop with Outlook/Win 7 for client. Mail server is Linux Ubuntu 10.10 (due for upgrade to 14.04 soon) - using Postfix+Dovecot. 1. Able to authenticate to server for smtp and pop using wifi at home and using 3G anywhere. 2. Unable to authenticate in workplace office (talking office building not Office software!!)- keeps asking for username and password when using mail.example.com.au in settings for outlook. (substitute for real domain name of course) 3. Able to authenticate as above if using ip number instead, which makes sense, since in office wifi and mail server on same subnet (192.168.1.X) Why would authentication not work using domain name instead of IP in workplace? This suddenly started about 1 week ago, and has been working fine for months before. Any idea? (I need a clear thinking mind here! Mine is clogged up with all sorts of possibilities... including NSA conspiracy!!) (Before I can tell the user his Outlook/Win 7 is screwed up, I want to eliminate other possibilities. The only thing he says has change is an antivirus software update) Cheers Daniel