Background:

We have created 2 Azure single-tenant apps with the same set of permissions (Mail.Send & Mail.ReadWrite) within the same tenant. As per Graph API’s documentation, we should be able to send emails of size upto 150 MB per email, through 1 app and 1 mailbox combination.

Link – https://learn.microsoft.com/en-us/graph/throttling-limits#outlook-service-limits

Problem:

Since the documentation mentions the combination, so ideally if we have 2 different Azure apps, then we should be able to send 2 separate emails of size 150 MB each (total 300 MB) within 5 minutes from the same mailbox.

But unfortunately, it does not work. We get a throttling error from Graph API-

{
    "error": {
        "code": "ApplicationThrottled",
        "message": "Application is over its IncomingBytes limit."
    }
}

Question:

When the documentation mentions the combination, then why is the API not allowing to upload more than 150 MB (2 separate emails) in the same mailbox within 5 minutes using 2 different Azure apps?

Example:

• Create Authorization token1 from App1.
• Create a draft email in mailbox1 and upload a 140 MB file using the upload session.
• Create Authorization token2 from App2.
• Create another draft email in the same mailbox1 and upload a 140 MB file using the upload session. It fails at this step with the above error.