Attachment dropped when sending mail using Graph API

Question

I am sending a mail using the graph API from a shared mailbox ([email protected]).

There is a .CSV file added to this POST call. The mail is sent with the correct subject and body. However, the attachment is dropped.

The format looks perfect like it should be. Does anyone know why this is being dropped, and how to fix this?

This is my body sent to the endpoint

https://graph.microsoft.com/v1.0/users/[email protected]/sendMail

Body:

{
  "saveToSentItems": "true",
  "message": {
    "attachments": [{
      "@odata.type": "#microsoft.graph.fileAttachment",
      "name": "data.csv",
      "contentBytes": "MYFILEINBASE64"
      "contentType": "text/csv"
    }],
    "message": {
      "toRecipients": [{"emailAddress": {"address": "[email protected]"}}],
      "subject": "Hello from runtime params",
      "body": {
        "contentType": "Text",
        "content": "This is a test mail body."
      }
    }
  }
}

Thanks !

How large is the file you are attempting to attach?

Marc LaFleur
– Marc LaFleur

2025-10-01 21:50:59 +00:00
Commented Oct 1 at 21:50 — Marc LaFleur
– Marc LaFleur, Commented Oct 1 at 21:50
I'd also suggest trying the mime type text/plain.

Marc LaFleur
– Marc LaFleur

2025-10-01 21:55:08 +00:00
Commented Oct 1 at 21:55 — Marc LaFleur
– Marc LaFleur, Commented Oct 1 at 21:55

andrewJames · Accepted Answer · 2025-10-02 00:06:02Z

1

The JSON you posted doesn't look valid you have the message property defined twice (eg you have a second message property after the attachment property)

It should be

{
  "saveToSentItems": "true",
  "message": {
    "attachments": [{
      "@odata.type": "#microsoft.graph.fileAttachment",
      "name": "data.csv",
      "contentBytes": "MYFILEINBASE64"
      "contentType":"text/csv"
    }],
      "toRecipients": [{"emailAddress": {"address": "[email protected]"}}],
      "subject": "Hello from runtime params",
      "body": {
        "contentType": "Text",
        "content": "This is a test mail body."
      
    }
  }
}

edited Oct 2 at 0:06

andrewJames

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answered Oct 1 at 23:54

Glen Scales

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1 Comment

J-V-D-A Oct 2 at 8:40

This did the trick, the mail comes through without error, but it silently drops the attachment like this. Thanks !

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