I have searched all over and could not find the solution to this problem for Plesk 10.3.1. I have sendmail configured and installed on my server (centos 5, php 5.3.8). The problem is, I cannot send mail using the mail() function to domains hosted within Plesk. The mail() function works fine when sending to domains not hosted within plesk. I have tested the Sendmail function through the command line and it sends fine other than to the domains hosted in Plesk. I have been told that this is a known issue in Plesk but I cannot find the answer. My email is hosted on an external server, not on the server hosted by Plesk. I'm sure that for whatever reasaon, Plesk is trying to send the mail locally because the domains are hosted in Plesk. I have disabled the mail server service on the server and unchecked the box for Plesk to manage the email. This did not fix the problem. Any advice on this is much appreciated!