Microsoft Outlook / Microsoft Graph

### App
Microsoft Outlook / Microsoft Graph

### Summary:
Exchange rejects Pipedream Connect Graph sends with 550 5.7.501 while Outlook Web sends succeed

### Details:
We are using Pipedream Connect's proxy to call Microsoft Graph v1.0 for a delegated Exchange Online mailbox. We create a new or reply draft, update its recipients/body, optionally attach a small file, and call POST /me/messages/{id}/send.

Graph accepts the calls, the message appears in the correct mailbox's Sent Items, and Exchange message trace shows Received -> Processed -> Not delivered. Exchange then generates an NDR for both same-tenant and external recipients:

550 5.7.501 Service unavailable. Spam abuse detected from IP range.
Marker: S(2017052602)

Tenant: ralfiio.onmicrosoft.com
Test sender: ralfi-test-03@ralfiio.onmicrosoft.com
External test recipient: tarzanclawsonmain@agentmail.to

Controlled results on 15 July 2026 (Australia/Sydney):
- Outlook Web: Test 03 -> same-tenant Test 01 delivered.
- Outlook Web: Test 03 -> external AgentMail delivered.
- Outlook Web: Test 01 and Test 02 controls delivered.
- Pipedream Connect / Graph exact reply with attachment: all recipients failed. MessageTrace ID 6b9852c1-dbcd-4f0a-d254-08dee2384f89.
- Same Graph reply with no attachment: all recipients failed. MessageTrace ID dc0922d9-de20-4e97-2724-08dee23d9b44.
- New Graph message, one external recipient, plain text, no attachment: failed. MessageTrace ID 88e2e830-9166-4194-acc0-08dee240ff31.

The traces report source IPs 20.190.151.37 and 20.190.152.152. Microsoft Defender Restricted entities contains zero users/connectors. Exchange has zero transport rules and zero connectors; forwarding is off.

This isolates the failure to the Pipedream Connect / Microsoft Graph path rather than the mailbox, recipients, attachment, message body, or tenant-wide outbound delivery.

Could you please:
1. Confirm whether there is a known Microsoft anti-abuse or reputation issue affecting Pipedream's managed Microsoft OAuth client or Connect proxy path.
2. Identify whether Microsoft could be associating these sends with a Pipedream application identity or shared service path.
3. Advise whether we should use a custom Microsoft OAuth client to bypass the managed client, or whether Pipedream can escalate/delist the affected path with Microsoft.

Please tell us what additional non-secret identifiers or trace evidence you need. We can provide the full sanitized NDR and Exchange event details.

### Screenshots:
No screenshots included

No repository file, test, or entry point is named. Start by locating the Pipedream Connect Microsoft Graph OAuth/proxy path, then compare its sends with the supplied Exchange message traces; done means determining whether the managed path is responsible and documenting the escalation or supported workaround.

Written by the indexing model from the issue text.