Installing EMPF patch
eMPF is now included in the qmail-toaster package. eMPF reads a set of administrator-defined rules describing who can message whom. An administrator can use it to create policies that accept/deny a user (or domain) to send or receive internal/external mails.
The policies are set in /var/qmail/control/policy.
For details on how to create the policy, you can read the following links:
Reminder for using Squirrel Web Mail
A.M. showing that something need to pay attention on using Squirrel Webmail getting error after installing eMPF patch and set up /var/qmail/control/policy:
a - the policy is blocking the destination or the receiver (always check policies twice - mybe more ;)
b - are you using smtp auth in squirrelmail? if not no message will pass because eMPF only allows users to send mail if they are authenticaded (this beahvior can be altered at compile time but advise against it). Check your squirrelmail settings.
c - are you using a second server for webmail? if so it cannot be in your smtproutes because that would brake things.