FAQ

catchAll users can't send email as user other than themself

To allow a catchAll user to send mail with the address used as recipient, the option aliases has to be used instead of catchAll.

For instance, to allow user@example.com to catch all mails to the domain example.com and send mails with any address of this domain:

mailserver.loginAccounts = {
    "user@example.com" = {
        aliases = [ "@example.com" ];
    };
};

See also this discussion for details.