As you may already know plesk by default uses qmail for handling emails. One of the things we have done is routed all our mail from our plesk servers to a email cluster for filtering in our data center. This allows us to have control of all inbound and outbound emails and is easy to maintain a small list of ips rather than maintaining a large list of ips that send mail across the board.

Here is what you do.

1. Using your favorite ssh application I would suggest putty if you can not find it go here and grab it.
http://www.pivotalweb.com/clients/downloads.php

2. login to your server using putty and ssh as root

3. cd to /var/qmail/control

4. using your favorite editor create a file called smtproutes it is not there by default in plesk qmail

5. once you are in the editor and have smtproutes opened type in :yourmailserver.com (using your own mail server that is) and then save this and exit out of the editor. What this just did is created a smtp route file that tells qmail for forward all outbound mail for your mail server to the designated ip and or hostname. You have to make sure that your smart relay is enabled to accpet mail from your sending ip or else it will not work.

6. Now issue the command # service qmail restart and thats it all of your mail from your plesk server will be pushing all mail to the smart host relay.

We have successfully implemented this method with almost 100% of our clients for outgoing mail from their servers. In essence it has helped us combat spam internally and protect our networks from being put on block lists and also allows us to conrol a few select ips for outbound mail rather than having to battle with other isp’s all the time to make sure mail is getting through to the receivers on the other end.

This outbound and inbound filtering together makes for a rock solid platform in combating spam and our users love it and so do we because it keeps our costs down.