Google Workspace catch-all makes SMTP RCPT checks meaningless

When checking whether an address exists via SMTP RCPT TO, always include a nonsense control address such as definitelynotarealuser99812@domain. On a catch-all Google Workspace domain, every address returns 250 2.1.5 OK ... gsmtp, including the control, so a 250 proves nothing about the mailbox. If the control gets 250, treat the domain as unverifiable by SMTP and rely on other evidence.