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Fix email delivery issues for error code 5.1.8 in Office 365

Problems sending and receiving email messages can be frustrating. If you get a non-delivery report (NDR), also called a bounce message, for error code 550 5.1.8, this article can help you fix the problem and get your message sent.

email user symbol

I got this bounce message. Help me fix it.

Administrator symbol

I'm an email admin; how can I fix this?

Why did I get this bounce message?

You received this bounce message with error code 5.1.8 because your account has been blocked for sending too much spam. Typically, this problem occurs because your account has been compromised (hacked) by phishing or malware.

I got this bounce message. Help me fix it.

First, you need to reset your password and scan your devices for malware. However, the hacker might have configured other settings on your mailbox (for example, created Inbox rules to auto-forward email messages or added additional mailbox delegates). So, follow the additional steps in How to determine whether your Office 365 account has been compromised.

And, you need to tell your administrator that you think your account was compromised. Your administrator will need to unblock your account before you can send mail.

I'm an email admin. How can I fix this?

The sending account may be compromised. You will need to:

For more information

Email non-delivery reports in Office 365

Still need help with a 5.1.8 bounce message?

Get help from the Office 365 community forums Admins: Sign in and create a service request Admins: Call Support
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