Why we only receive

Regular CatMail mailboxes can't send mail. That's on purpose.

A mailbox that can only receive has no outbox to leak and can't be used to send spam in your name. It's a good fit for sign-ups, verification codes, and the mail you actually want to keep.

Only the service's own addresses (like support@) can send. If your mail app is set up with our outgoing server, it will accept the connection but decline to send — and tell you so, instead of pretending a message left.