Glossary · Mailboxes
A catch-all accepts email sent to any address at a domain, even ones that were never set up, and delivers it to one mailbox.
It means mistyped addresses still reach you, but it also accepts every guess a spammer makes, so catch-alls attract a lot of junk. It makes it impossible for senders to tell real addresses from fake ones, which list-cleaning tools treat with suspicion.
Most teams are better served by explicit aliases for the addresses they actually use. SuperMailOS has no catch-all: mail to an address that isn't a mailbox or an alias is rejected, so the sender gets a bounce.
Every domain you run in one inbox, from $3 a mailbox. 14 days free, no card.