I have setup mailcow as a spam filtering server only and I RELAY ALL to some other servers. For the quarantine to work, I need to create manually all the mailbox and assign them passwords which is a lot of work to do and a waste of time. Could you automatticaly create mailbox accounts in a “spam firewall mode” and send a welcome message with their passwords to the users. Baracuda spam firewall are working like this and at some point, I go in the spam firewall and launch a cleanup process that check each email existance on the destination server and if the response is negative (check the response of the MAIL TO: of the server and get an error) then remove that mailbox(quarantine) from the mailcow server.