Exchange Online Email delivery Needs an admin

550 5.4.1: recipient address rejected, access denied

Likely causes

• The recipient address is misspelled or doesn't exist.
• The recipient exists on-premises but isn't synced to Exchange Online (hybrid).
• The recipient is a mail-enabled public folder or dynamic distribution group that Exchange Online doesn't know about.
• MX or DNS records point to a server that doesn't accept mail for the domain (Relay Access Denied).

How to fix it

1. Check the address in the bounce for typos and send again.
2. Work out the scope: one recipient, or every address in the domain? One recipient points to that object. The whole domain points to domain or DNS setup.
3. Admins: confirm the recipient exists in Exchange Online. For hybrid users, check directory sync is working and the proxy addresses are right.
4. Admins: check the domain’s MX record points to Exchange Online and the domain is an accepted domain.
5. Admins in hybrid: Authoritative domains reject unknown addresses. Only use Internal Relay if a connector routes unmatched mail to your on-premises servers.

Checked against: learn.microsoft.com, support.microsoft.com