Block permissions to send as this sender

[saitobenkei]

Maybe this helps:

Enable SMTP Login/Sender address validation

Thanks to @stephdl it is now possible to Check authenticated user/identity before sending ¹: current SMTP/AUTH login name must be authorized to use a sender address. Imagine that we have the user joe and the account domain example.com. The following rules apply: User joe can write as joe@example.com If joe is listed as recipient in the email alias sales@example.com he can also send messages as sales@example.com Similarly, if joe is recipient for email alias joe.brown@aliasdomain.com he can…