Microsoft Graph Webhook Filtering Using Custom MAPI Properties for Weather Messages

Hi everyone,

I'm working on an integration that uses Microsoft Graph change notifications (webhooks) to receive notifications for new email messages in a mailbox.

Our use case is specific to Weather messages generated by our Messaging platform. Currently, we subscribe to mailbox notifications and receive events for all incoming emails, which results in significant post-processing on our side.

I'm looking for a way to perform server-side filtering so that only Weather-related messages trigger webhook notifications.

Current Situation

We use Microsoft Graph webhook subscriptions on mailbox messages.

Weather messages are delivered as standard emails.

Subject-based filtering is sufficient for our requirements.

We would like to avoid processing every incoming email after receiving notifications.

Proposed Approach

We are considering stamping weather emails with a custom MAPI extended property when the message is created, for example:

Message subject   = Weather

using a custom single-value extended property.

Questions

Can Microsoft Graph webhook subscriptions filter notifications based on custom MAPI extended properties?

If not directly in the subscription, can $filter be used on message queries against these custom properties after receiving notifications?

Has anyone successfully implemented a solution where a custom MAPI property acts as a service tag for weather messages?

Are there any recommended alternatives for reducing webhook traffic when only a subset of messages is relevant?

Would Outlook categories, message classes, or other Exchange attributes provide a better filtering mechanism than custom MAPI properties?

Our goal is to identify weather messages reliably while minimizing unnecessary webhook notifications and mailbox processing.

Any guidance, examples, or best practices would be greatly appreciated.

Thanks!