email bounce back

Joey Yu 0 Reputation points

Dear Sir,

My email bounced back with following response which happened in certain emails

Your message couldn't be delivered. Despite repeated attempts to contact the recipient's email system it didn't respond.

Contact the recipient by some other means (by phone, for example) and ask them to tell their email admin that it appears that their email system isn't accepting connection requests from your email system. Give them the error details shown below. It's likely that the recipient's email admin is the only one who can fix this problem.

For more information and tips to fix this issue see this article:

Outlook Management
Outlook Management
Outlook: A family of Microsoft email and calendar products.Management: The act or process of organizing, handling, directing or controlling something.
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  1. Joey Yu 0 Reputation points

    Dear Sirs,

    Same problem happened to my colleagues as well, we all have same error code as below for particular email.

    Remote server returned '550 5.4.300 Message expired -> 451 This mail has been deferred because the sender is sending too much mail for its authentication status. Please set up DKIM aligned to the From: domain. See for more information.'

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  2. Faery Fu-MSFT 17,811 Reputation points Microsoft Vendor

    Hi @Joey Yu ,

    From 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 yahoo account.

    You may also contact your Microsoft 365 admin to find out what happened to an email message by running a message trace in the Exchange admin center. For more information, see Message trace in the modern Exchange admin center.

    In addition, I found a similar thread that mentioned the issue may be caused by that Yahoo had identified Microsoft as "abusive”. This is the issue between Yahoo and Microsoft, instead of your issue. All emails I am attempting to send to Yahoo/Aol accounts are bouncing - Microsoft Community

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