How to prevent receiving e-mail where the from address is from a blank or non-existing internal user?

[Ricardo Ruggiero]

Just wondering how to deal with the following situation (using Kolab 2.3.4):

We are beginning to receive email (spam) to a someone in our Kolab server,
and the from address is a forged internal address.

For example:

tom at mydomain.com (a legit user) receives an e-mail from "
accounting at mydomain.com". The "accounting at mydomain.com" does not exist.

another example that we would like to filter is when the sender is blank.

Thanks.

Ric Ruggiero
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