In order to have greater control over the emails sent out the company I imagined the following scenario.
Describing in words what I need.
User sends an email to firstname.lastname@example.org
for example, using the smtp of my isp (is the internet).
Before the email is sent, the firewall checks
if the recipient is blocked transparent
, if you are locked out rejects the email.
I searched several forums and mailing lists, but did not find scenarios similar to mine.
Where found situations in which the mail servers were internally in the company, which is not my case.
I have no control over the smtp of my isp.
I do not need a howto, just a direction how to proceed.
Thanks for your help!