When sending emails using Microsoft Graph API, what's the correct way to send more than 150 MB within 5 minutes?

Question

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 when trying to draft 2nd email-

{
    "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.

Answer 1

Hi @Piyush Chugh

According to the restriction documentation, you can know that the limit is an Outlook service limit, not a Graph API limit, and the maximum upload of a mailbox in 5 minutes is 150MB, so 2 applications cannot make a mailbox upload more than 150MB in 5 minutes.

What is possible, however, is that an application can upload files up to 150MB in 5 minutes from 2 different mailboxes simultaneously.

Therefore, it is impossible to upload two 140MB files in the same mailbox within 5 minutes at the same time. The feasible solution is:

1. You can use one application to control the upload of two mailboxes at the same time
2. Use one email address to upload files, but upload files in sequence. After uploading a file, wait for more than 5 minutes before uploading another file.

Hope this helps.

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