550 5.1.1 and 550 5.1.10: Exchange Online cannot find the recipient
550 5.1.1 and 550 5.1.10 mean the recipient address does not resolve in Exchange Online. Check for deleted, unlicensed or mistyped mailboxes first.
550 5.1.1 and 550 5.1.10 mean the recipient address does not resolve in Exchange Online. Check for deleted, unlicensed or mistyped mailboxes first.