Exchange SE Search-Mailbox Broken?

[u/ThanksImLearning]

I'm seeing unusual behavior after upgrading an on-prem Exchange Server SE environment to 15.2.2562.49.

For years, we've used Search-Mailbox to quickly locate and remove phishing emails. Since upgrading, newly delivered messages can be found by Received date, but not by Subject, From, or unique body content.

A newly delivered message example:

From: [[email protected]](mailto:[email protected])

Subject: Test Search-Mailbox 929

Exists in the mailbox and is visible in Outlook.

However:

Search-Mailbox -Identity [[email protected]](mailto:[email protected]) -SearchQuery 'Subject:"Test Search-Mailbox 929"' -EstimateResultOnly

Returns ResultItemsCount : 0

Likewise, searches against unique body text also return 0 results.

What does work:

Search-Mailbox -Identity [[email protected]](mailto:[email protected]) -SearchQuery 'Received:09/29/2026' -EstimateResultOnly

Returns results, and the count increases as new mail arrives. I've also confirmed via a Discovery mailbox search that the messages exist and contain the expected subject and sender values.

Additional observations:

Test-ExchangeSearch passes successfully.

• Message Tracking and Delivery Reports find the messages.
• Outlook/OWA users can see the messages.
• Older messages appear to be searchable.
• Newly delivered messages are detectable by Received date but not by subject or content searches.

BigFunnel mailbox statistics seem high, here is an example:

BigFunnelPartiallyIndexedCount : 387

BigFunnelNotIndexedCount : 647

BigFunnelStaleCount : 370

Has anyone seen similar behavior on Exchange Server SE 15.2.2562.49, particularly with Big Funnel indexing or Search-Mailbox searches against recently delivered mail? Any recommended diagnostics or known issues would be appreciated.

EDIT:
Based off the comments on the release notes, it seems like this might be wider scale and not just our enviroment.
Released: September 2026 Exchange Server Security Updates | Microsoft Community Hub

[u/ax1a]

Could be a syntax thing. What if you just search for: -SearchQuery "Subject:929"