Outlook emails not deliverable to yahoo and aol

Hi

Good day!

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Microsoft Community

Hello HRW Realty Team,

Thank you for posting this case in Microsoft Community!

Based on your description: Outlook emails could not be sent deliverable to yahoo and AOL account. I would like to cooperate with you working on this case. To clarify this case, as checked your NDR bounce message, the email took too long to be successfully delivered to yahoo and aol account. You may check this Microsoft article about error code 5.4.300 Message expired. Email non-delivery reports and SMTP errors in Exchange Online

For my suggestion, firstly you may check if set up SPF, DKIM and DMARC for your custom domain in Microsoft 365 completely. You may check this Microsoft article as reference:

Enhanced Filtering for Connectors in Exchange Online

Set up SPF to help prevent spoofing

Please also make sure if your network bypassed Office 365 URLs and IP address ranges which help to deliver email to yahoo and aol account. For extra report information from backend side, you may also contact your Microsoft 365 admin to check message tracing if getting more useful details about why you could not send out emails to yahoo and aol account normally Message trace in the modern Exchange admin center in Exchange Online.

For further assistance, you may contact Microsoft Technical Support Team with a ticket opened: Ways to contact support for business products - Admin help. Go to Office365 admin center>Support>New Service Request. The support team over there has higher permission than us, they can remotely help you and collect logs at your convenience. They can also involve more resources to investigate the issue from backend side. This would be the most efficient way in handling this case for you.

(Note: Admin permission required to open the ticket with Microsoft Technical support team, so if you are not admin/no admin permission, kindly contact your admin, If you purchased Microsoft subscription from Microsoft partner, it is recommended to contact your partner to open the ticket.)

Your understanding and patience will be appreciated.

Thank you!

This is the exact problem I am having starting last week...to aol and yahoo addresses I had successfully used before. And I was unaware for a while because the notice of being undeliverable went into MY junk holder. Even after I added the Microsoft email address to my safe list in Outlook. HELP.

I'm having this issue as well. Do you use a service called mailgun by chance? Trying to pinpoint it as the cause or something else. TIA

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