Message size issue

Sree 1,971 Reputation points

Message size upto 25 MB are allowed by rules. But even 19 MB is getting rejected..
I want to allow 25 MB attachment size in the email please advise

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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Exchange Server Management
Exchange Server Management
Exchange Server: A family of Microsoft client/server messaging and collaboration software.Management: The act or process of organizing, handling, directing or controlling something.
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  1. Jade Liang-MSFT 9,976 Reputation points Microsoft Employee

    Hi @JustinMicheal-7973 ,

    Message size upto 25 MB are allowed by rules. But even 19 MB is getting rejected..

    Please first understand for the message size limit, you need to set a value that's larger than the actual size you want enforced( base64 encoding increases the size of the message by approximately 33%). For more information, please refer to it: For any message size limit.

    So if you would like to allow the messages with 19MB, we need to set the limit greater than 26MB(19MB+19MB*33%).

    Besides, if the issue still exists when you set a larger limit, agree with michev, there are many other limits that could also reject the messages(message size limit on mailbox,message size limit in organization, message size limit in connector). It's recommended to follow the document above to check the message size limits on mailbox and your organization to confirm if the message exceeds the scope of other limits.

    If I have any misunderstandings or you still need further assistance, please provide us with more information about your limit configuration to further analyze your issue.

    If the response is helpful, please click "Accept Answer" and upvote it.
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  1. Vasil Michev 100.2K Reputation points MVP

    Is this for on-premises Exchange? Where have you changed the settings, as those can be configured on several different "scopes" as detailed here:
    Also note that the "message" limit is not the same thing as the "attachment" limit, and there are also client-side limits to consider: