Email delivery failed to Gmail addresses only

Question

Can someone tell me why my emails are bouncing back from gmail recipients only? Diagnostic information below.

Diagnostic information for administrators:

Generating server: SN7PR18MB4400.namprd18.prod.outlook.com
Total retry attempts: 14

Remote server returned '550 5.4.300 Message expired -> 421 4.7.28 [2a01:111:f400:7e8a::600 15] Our system has detected an unusual;rate of unsolicited mail originating from your IP address. To;protect our users from spam, mail sent from your IP address has been;temporarily rate limited. Please visit; https://support.google.com/mail/?p=UnsolicitedRateLimitError to;review our Bulk Email Senders Guidelines. l27-20020a170906079b00b009a1bc22b472si4259684ejc.1017 - gsmtp'

Answer 1

Hi @Laura Sims,

Are you using Exchange Online or Outlook.com as your email service?

From the NDR message the issue is with backend.

If possible please contact Microsoft support for further investigation.

Exchange Online: contact the global administrator in your organization to open a service request in Microsoft 365 admin center>Support>Help & Support.

Outlook.com: How to get support for Outlook.com

Thanks for your understanding.

---

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment". 

Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.