Graph API sending email problems

[iunir]

Hello,

Having a web app, I would like to be able to send email on behalf of users.
Users of my app are only corporate. I prefer to use auth_flow_type=='credentials'.

I've managed to write a script. Authorisation part passes successfully and I'm receiving the token.
But send fails.

If I'm using the user_id as resource:

Client Error: 400 Client Error: Bad Request for url: https://graph.microsoft.com/v1.0/{{THERE_IS_CORRECT_USER_ID}}/sendMail | Error Message: Resource not found for the segment 'sendMail'. 

If I'm using email:

Client Error: 404 Client Error: Not Found for url: https://graph.microsoft.com/v1.0/users/{{THERE_IS_CORRECT_EMAIL}}/sendMail | Error Message: The requested user '{{THERE_IS_CORRECT_EMAIL}}' is invalid.

The permissions are set:

I've also tried to do same using official Postman collection. Using email as resource provides me same result. But with user_id I'm getting:

    "error": {
        "code": "MailboxNotEnabledForRESTAPI",
        "message": "The mailbox is either inactive, soft-deleted, or is hosted on-premise."
    }
}

Also, I was able to list the users through API (I've took user Id from there).

Asking of help. What can be the reason?

UPDATE
I've found it's not using users/ before user_id, while using email as a resource it adds it automatically.
Now I have same: The mailbox is either inactive, soft-deleted, or is hosted on-premise from my Python.

So, how to fix that problem?

[alejcas]

I think it's because you need to set the permissions to "delegated" and not "application".

can you triy this?

[iunir]

Thanks a lot @alejcas for quick response.

I've tried to set all possible Delegated permissions:

But still same error. BTW in my understanding Application permissions for auth_flow_type="credentials" and Delegated permissions for authorising On behalf of a user. Please correct me if I'm wrong.

[iunir]

Finally. After about 1 week of struggling. Office 365 license (business type, bought and assigned by admin) helped.
I've tried with @outlook.com user, bought private license, but not worked. Funny fact, Microsoft promised to give me 30d free, but charged first second.
Also tried Microsoft Entra ID P2 license. Which did not help as well.

[alejcas]

There seems to be a limitation on delegate permissions with personal accounts