Block email faking to be from our domain but coming from outside?

[William D. Colburn]

On Fri, Jun 08, 2018 at 02:18:02PM +0200, Remco Barendse wrote:
>Thanks for your reply!  These are not bulk spam messages, I'm talking
>carefully engineered tailor made messages from someone imposing to be
>myself and trying to persuade someone in finance to make a payment or
>change bank details.

Have your mail servers add a header to all mail originating on the
inside, and then use a spamassassin ruleset to flag all the messages
that look like they are from the inside but lack that header.


--Schlake