The easiet/surest way is to use ASMTP = only relay if the sender can authenticate. Using IP restrictions to relay can be abused if network is compromised.
This is a generic solution which is applicable to ALL situations - until one of your users uses a useless password, then you are screwed!


On 26 July 2016 at 22:50, Dennis Mugaya via skunkworks <skunkworks@lists.my.co.ke> wrote:
Hi
My mail server(squirrel mail,postfix and dovecot) is relaying messages from other user accounts that are not registered in my server how do i stop these relay messages. Its my first time to configure a mail server kindly assist am learning.

Regards

--
Dennis Mugaya
Network Administrator


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"Oh, the cruft."