550 From Address Violates UsernameCaseMapped Policy: What It Really Means (And How to Fix It Fast)
You send an email expecting it to reach the recipient without any problems. Your domain authentication is set up correctly. The content looks normal. There are no clear mistakes, and everything seems fine from your side. But instead of being delivered, the email returns a hard bounce message: 550 From address violates UsernameCaseMapped policy. This…
