I decided to rebuild my Linode with the latest Ubuntu 14.04 LTS and setup everything from scratch. I followed this guide: http://www.howtoforge.com/perfect-s...hp-mysql-pureftpd-bind-dovecot-ispconfig-3-p4 I'm not receiving e-mails and I'm not able to send any. After composing a mail using SquirrelMail 1.4.23 [SVN], I get an error: "ERROR: Message Not Sent. Server Replied:" I don't even know how to start diagnosing. Please, suggestions?