Attachment size

Question

I am using exchange se edition hybrid env. we create users onprem and migrate to online.One of our users is unable to send an email with a 34 MB attachment (PowerPoint file). I have explained that Exchange uses Base64/MIME encoding, which increases the message size by approximately 33% during transmission, potentially exceeding the configured message size limits.

However, the user reports that another team member is able to send the same file without any issues. I am unsure how this is possible. What areas should I check to identify why one user can send the attachment while another cannot?

Answer 1

Hi @Glenn Maxwell

From the details you provided, I understand that one of your users in an Exchange SE Hybrid environment is unable to send a 34 MB PowerPoint attachment due to message size limits after Base64/MIME encoding, yet another team member can send the exact same file without any issues.

After researching this, Exchange does not just rely on a single global limit. Email size limits are applied at multiple levels (such as Mailbox, Transport, or Connector levels) and can actually differ between two users in the same environment.

First, according to the documentation I found, the maximum email size a user can send or receive also heavily depends on the specific email client they are actively using.

You can refer to the following documentation for more details on client limits:

Message limits

Because of this, could you help me check exactly which email clients both of these users are using to send the file?

Besides that, please try checking the individual send/receive limits configured directly on each user's mailbox by running the following PowerShell command:

Get-ExoMailbox userA,userB | Format-List MaxSendSize,MaxReceiveSize

Please let me know what you find out so we can narrow down the issue!

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