Exchange/365 attachment size message different between clients

Vince Viking 21 Reputation points

When you try to attach a file above the exchange limit of 34MB the outlook client will warn with a message such as "the email message cannot be sent because it exceeds the 35MB outgoing message size limit"

I have noted windows mail and owa will say 33MB, Windows Outlook client will 35MB and Mac can be different again using the same email account. The actual limit is 34MB.

I need an actual explanation/reason why this is and why windows mail/outlook web would state the limit is 33MB and Outlook windows client would state 35MB when trying to attach a file over the limit.

This is so I can explain why different numbers are displayed depending on client when the actual limit set is 34MB as part of some research I am doing.

Outlook Management
Outlook Management
Outlook: A family of Microsoft email and calendar products.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.
7,227 questions
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  1. Leon Laude 85,566 Reputation points

    Hi @Vince Viking ,

    Please note that is currently not supported in the Q&A forums, the supported products are listed over here

    You may ask the experts in the dedicated forum over here:


    (If the reply was helpful please don't forget to upvote and/or accept as answer, thank you)

    Best regards,

    1 person found this answer helpful.
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  2. Zhengqi Lou-MSFT 8,856 Reputation points Microsoft Vendor

    Hi @Vince Viking ,

    Good day!

    As Leon said, the .com accounts are not supported by us, we mainly talk about Exchange and other outlook client questions based on the tag.

    Could you tell me how you set the limit for Exchange to 34MB? Using Set-TransportConfig or other cmdlets?
    And also what's the Exchange version in using, is it on-prem or online?

    Based on my knowledge, the default setting for OWA is, Outlook on the web
    maxAllowedContentLength="35000000" (byte) so it's about 33 converting to MB. You could change it by manually changing the value in Web.config file.

    Best regards,

    If the response is helpful, please click "Accept Answer" and upvote it.
    Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.

    1 person found this answer helpful.

  3. Vince Viking 21 Reputation points

    Thanks - Take the aspect out and make it more generic then, if attachment limit is set 34 on exchange, why would outlook client say 35MB whilst owa 33MB?

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  4. EileenB 1 Reputation point

    I think it is the mathematical thing (check MB for MegaByte and MiB for Mebibyte).

    The real question is - why are you depending to send the full 35 MB? Outlook may support it, but does the service, does the recipient (recipients service / recipients mail client) also support this? Is the security level good enough for this scenario?

    I am not sure if there is an actual rule, but I'll stick to the 10 MB border, as for mail. It isn't meant to transfer those masses.

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