Hello and thanks for the howto. I've been using this mailserver setup for a few years now, but recently I noticed that some of the recipients MTA reject messages when sent from an email client like Tunderbird or Outlook Express. The difference between a message sent from a client and the one sent from horde is in the Sender name. From Horde is correct - email@example.com From mail a client is wrong - "firstname.lastname@example.org"@mail.example.com, where mail.example.com is the hostname of my mail server. The complete line in log file (real user and domains changed): Code: 2010-08-10 11:37:07 1OikKS-0002Tp-M2 <= "email@example.com"@mail.example.com H=([192.168.1.103]) [188.8.131.52] P=esmtpa A=plain:firstname.lastname@example.org S=984 id=4C610FA8.email@example.com I googled for a few days untill I found no solution to this problem. Please help if you have any ideas.