Outlook Node Schema Validation Issue with MCP Agent

[Kiremit]

---

Hi n8n community!

I’m facing an inconsistency between Gmail and Outlook nodes when using them with the AI Agent.

Setup:

• AI Agent calls Outlook node via MCP server
• CC/BCC fields set to “Defined automatically by the model”

Issue:

• Gmail node: Works fine even when AI doesn’t provide CC/BCC values
• Outlook node: Throws “Received tool input did not match expected schema” error when CC/BCC fields are empty

Error message:

At least one recipient is not valid. Recipient '' is not resolved. All recipients must be resolved before a message can be submitted.

Problem:

• If I don’t add CC/BCC fields → Can never use CC/BCC
• If I add CC/BCC fields with “Defined by model” → Microsoft ALWAYS EXPECTS VALUES THERE - CANT BE EMPTY. GMAIL DOES NOT!!!

Question: Is there a way to make Outlook node handle optional CC/BCC parameters like Gmail node does? Or any workaround to make CC/BCC truly optional when using AI Agent?

Thanks for any insights!

Information on your n8n setup

• n8n version: 1.99
• Database (default: SQLite): SQLite
• n8n EXECUTIONS_PROCESS setting (default: own, main): own
• Running n8n via (Docker, npm, n8n cloud, desktop app): Docker
• Operating system: Windows 11

[cutecatcode]

Hello, can you show us the AI Agent system prompt?

Maybe you can do some tweaking in AI Agent system prompt to make the AI more understands what you need.

Some AI model needs to be more understand with the system prompt.

Lmk if it helps

[Kiremit]

system prompt shouldnt have anything to do with it: “Send a message in Outlook from the private Outlook/Microsoft Account of Sven”

it works perfectly fine once I pass a cc and bcc in the prompt. If only one or none it does not. Thats the problem.

[cutecatcode]

Ok. I got it.
Try this simple solution.

Add description to each field that important. Like BCC Recipients and CC Recipients field.
You can add desc to “make the bot know that the fields just additional, not important”

[Kiremit]

This does not work. As soon as you add the fields with outlook it expects a value.

[hemzet]

@Kiremit We’ve confirmed this issue isn’t related to using an Agent. Our team is migrating from the Send Email (SMTP) node to the Outlook node (since we now need OAuth), and we’ve noticed a major gap in usability.

Unlike the SMTP node, the Outlook node treats all optional fields (e.g., CC, BCC, Attachments) as mandatory once they are defined - they can’t be left empty or null. This creates real challenges for low-code workflows and reusability: instead of one flexible node that can handle multiple scenarios, we’re forced to branch logic or duplicate nodes to cover each case.

Feature request: Making optional parameters in Outlook node optional
It would be great if the Outlook node could be adjusted so that optional fields truly remain optional. This would bring it in line with the behavior of the SMTP node and better support low-code design.