It's frustrating when you get an error after sending an email message. This topic describes what you can do if you see error code 550 5.1.0 or 5.1.0 in a non-delivery report (also known as an NDR, bounce message, delivery status notification, or DSN).
The destination email server that generated the 5.1.0 error won't accept messages from you (the sender) or messages for the recipient. This can happen if messages from you (your email address, your Exchange Online organization, or even all of Exchange Online) are being blocked by the recipient.
This section contains steps that you can try to fix the problem yourself.
If these steps don't fix the problem for you, contact your email admin and refer them to this topic so they can try to resolve the issue for you.
Your email address could be in the recipient's personally-maintained block list. This is the likely cause if you can successfully send messages to other recipients in the same domain (for example, @fabrikam.com).
Contact the recipient (by phone, in person, etc.) to verify that your email address isn't in their block list.
The Sender Policy Framework (SPF) record for your Exchange Online domain might be incomplete, and might not include all sources of mail for your domain. For more information, see Set up SPF in Office 365 to help prevent spoofing.
User information section: Address Rejected. A problem occurred during the delivery of this message to this email address.
Diagnostic information for administrators section: Recipient address rejected: SPF Permanent Error.