outlook.com problem "Server busy. Please try again later from"

Question

Sice today morning we have many e-mails on outgoing queue, where is similar part:

....eu.mail.eo.outlook.com[102.51.8.44] said: 451 4.7.500 Server busy. Please try again later ....

I mentioned, that this seems to be global problem as in forums are discussed about this also.

If this is somehow related with certain sender IP-addresses, then where is the place, where I can report, that my IP-s can be released from blacklist, if they are there at all.

Actually tag "Exchange online management" was put only, that something needed to enter there.

My ip server is 187.44.166.250 no blacklist

Answer 1

Hi @Rafael Leão ,

What’s your Exchange environment? Is it an Exchange online environment or a hybrid deployment environment?

Did you change any settings on your Exchange server before this issue occurred?

According to the Microsoft official article, this error code is part of anti-spam filtering in Microsoft 365 or Office 365. You'll get this error when the source IP address that's sending you email changes significantly from its previously-established patterns. This error response is called IP throttling, and it can help reduce the amount of spam that you receive.

Please try the following solutions provided by Microsoft official: Fix email delivery issues for error code 451 4.7.500-699 (ASxxx) in Exchange Online

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Answer 2

My scenario is a Zimbra Collaboration 8.8.15 server, I can send to all boxes instantly and with Outlook, specifically for corporate accounts or even it takes 5 hours to send.

Are you experiencing any blockages? I have functional SPF, DMARC and DKIM