451 4.7.500 Server busy (S77719)

sanjay 1 Reputation point
2021-02-03T17:15:03.883+00:00

Could anyone please let me know how to resolve 451 4.7.500 Server busy (S77719) problem. We are unable to send any emails to our clients/customers.

Office Development
Office Development
Office: A suite of Microsoft productivity software that supports common business tasks, including word processing, email, presentations, and data management and analysis.Development: The process of researching, productizing, and refining new or existing technologies.
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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.
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  1. Lucas Liu-MSFT 6,161 Reputation points
    2021-02-04T02:42:51.467+00:00

    Hi @sanjay ,
    What’s the your Exchange environment? Is it a pure Exchange online cloud environment or a hybrid deployment environment that includes on-premises Exchange?
    Did you change any settings of Exchange server before this issue occurred?

    1. Please check that your Exchange server and IP does not appear on any block list.
    2. According to the Microsoft official article, this error code is part of anti-spam filtering in Microsoft 365 or Office 365. When the source IP of your emails or the mode of your emails (for example, sending a large number of emails suddenly), then you may receive this error. 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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