Error 550 5.4.300 and 421 4.4.2 when sending to email address

Maureen Kauffman 20 Reputation points

I am getting message 550 5.4.300 and 421 4.4.2 when sending email to account. I checked with recipient and I am not on their blocked senders list.

I updated to windows 11 to see if that helped. no luck.

Microsoft Office Online Server
Microsoft Office Online Server
Microsoft on-premises server product that runs Office Online. Previously known as Office Web Apps Server.
579 questions
Microsoft Exchange Online Management
Microsoft Exchange Online Management
Microsoft Exchange Online: A Microsoft email and calendaring hosted service.Management: The act or process of organizing, handling, directing or controlling something.
4,150 questions
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Accepted answer
  1. Jayce Yang-MSFT 1,246 Reputation points Microsoft Vendor

    Based on your description, please kindly check if set up SPF, DKIM and DMARC for your custom domain in Microsoft 365 completely. Please also make sure if your network bypassed Office 365 URLs and IP address ranges which help to deliver email to aol account.

    If all configurations are correct, and you only have this issue with AOL and Yahoo accounts, based my previous experience, this issue may be caused by that Yahoo had identified Microsoft as "abusive”. This is the issue between Yahoo and Microsoft, instead of your issue.

     Some similar thread:

    All emails I am attempting to send to Yahoo/Aol accounts are bouncing - Microsoft Community

     You could contact Microsoft Support to report this issue: Get support - Microsoft 365 admin | Microsoft Learn

    Or ask the administrator of your email domain to [submit a request to the AOL Postmaster support team]("Visit our help page to submit a Sender Support request."). Why can't I send mail to AOL Mail users? - AOL Help

     If this answer helps you please mark "Accept Answer" so other users can reference it.


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