I’m interested on restricting some mailbox from sending email to other domains. I must say that I have been playing with mailcow for a couple of days but cannot achieve it.
Lets say I have a couple of users @mailbox1.com
user1… email@example.com can email to each other only
any external email sent to user1… firstname.lastname@example.org needs to be delivered to userX@mailbox1.com
email@example.com can send to firstname.lastname@example.org
Any help will be much appreciated.