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Gets a "452 4.5.3 Too many recipients (AS780090)" error

Lior Tomer 25 Reputation points
2024-08-21T12:26:50.9266667+00:00

Please help me,

Starting on Friday, August 16, 2024, any message sent to more than one recipient receives a "452 4.5.3 Too many recipients (AS780090)" error for all recipients except the first one. This leads to unnecessary message duplication, increased workload on our filtering system, and flooding of the history, quarantine, and event logs. We are seeing the same behavior in another test installation of our system at a different location, which began on the exact same date. Previously, all messages were accepted by Exchange 365 without issues, regardless of the number of recipients.

It seems to be some form of throttling intended to control spam. However, our primary goal is to sanitize content and reduce spam at the file attachment level.

Can we somehow get whitelisted?

Why an encrypted inbound SMTP connector, which is created for us by O365 tenant itself, means nothing?

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  1. Anonymous
    2024-08-22T07:14:33.35+00:00

    Hello, @Lior Tomer,

    Welcome to the Microsoft Q&A platform!

    Based on your description, I understand that any message you sent to more than one recipient has received a "452 4.5.3 Too many recipients (AS780090)" error for all recipients except the first one since last Friday. 

    To find out more precisely what the problem is, I would like to ask you some questions:

    1. Have you recently changed your system settings?
    2. What is the approximate number of recipients of your email?
    3. Can you send emails to internal recipients normally without using the SMTP connector?

    At the same time, you can use the Get-OutboundConnector command in PowerShell to view configuration information for the outbound connector.

    In order to whitelist the domains and email addresses you need,  please follow the steps below in Microsoft Defender.

    A screenshot of a computerDescription automatically generated

    User's image

    About how to use PowerShell for the same purpose, you can refer to this document: Allow or block email using the Tenant Allow/Block List - Microsoft Defender for Office 365 | Microsoft Learn.

    Regarding the encrypted inbound SMTP connector that your O365 tenant creates for you, Office 365 applies anti-spam and anti-abuse measures even when using an encrypted inbound SMTP connector. Encryption ensures data privacy in transit, but does not bypass other security protocols.

    In order to solve your problem more effectively, I hope you can take the time to reply to me! Accept the answer if the information helped you. Thank you for your support and understanding.

    Best Wishes,

    Alex Zhang

  2. JUAN SALDA 35 Reputation points
    2025-11-11T14:07:14.4866667+00:00

    Microsoft y sus ridiculas politicas con el fin de ordeñar los bolsillos de sus clientes

    Te regalan el candado y luego te venden la llave... Cuanto vale la suscripciona defender? no les da ni pena!!

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