Windows Search full-text index lacks most Outlook Classic mail content with Copilot+ PC

TITLE

Windows Search full-text index lacks most classic Outlook mail content on one PC; identical PSTs index fully on another PC (same Windows and Outlook builds)

CATEGORY

Search (Desktop Environment > Search, or nearest equivalent)

SUMMARY

Two PCs run the same Windows build and the same classic Outlook build, with identical PST files and the same mail accounts. On one, the Windows Search full-text index returns about 6% of the content matches found on the other. The mail items and their properties are indexed on both (subject-search counts are identical). The problem survives index rebuilds, a new Outlook profile, and re-copying the PSTs.

ENVIRONMENT

• PC A (affected): ASUS ProArt P16 H7606WP, Copilot+ PC with NPU
• PC B (unaffected): desktop without an NPU
• Both: Windows 11 Pro 26H2, OS build 26300.9457, Windows Feature Experience Pack 1000.26100.360.0
• Both: Microsoft 365 classic Outlook, 64-bit, same build and settings
• Mail: five PSTs of roughly 1 GB each plus OST-backed accounts, identical on both PCs (PSTs copied from B to A, then repaired with scanpst on both)

EVIDENCE

Queries against the Windows Search index in 64-bit PowerShell

(Provider=Search.CollatorDSO, SystemIndex, System.Kind='email'), word "constitution",

run after a full index rebuild on both PCs:

                                         PC A     PC B

Subject LIKE '%constitution%' 28 28

CONTAINS(System.Subject,'constitution') 28 28

CONTAINS('constitution') (any column) 15 269

• On PC A the any-column count (15) is lower than the subject-only count (28). Assuming an any-column search covers the subject, at least 13 emails whose subject contains the word are missing from the full-text results although their properties are indexed.
• Full-text matches by store (PC B vs PC A):

Store PC B (desktop) hits PC A (laptop) hits

PST 1 (main) 103 0

PST 2 (archive, oldest) 48 11

PST 3 (archive) 23 2

PST 4 (archive) 40 0

PST 5 (archive, newest) 26 2

Account mailboxes

(OSTs, combined) 29 0

Total 269 15

The shortfall is near-total in every store,

including the PST 4 (40 vs 0), where both PCs list the same

number of items.

• Loose .msg files saved to a local folder are content-indexed normally on PC A. Only items read through the mapi16 handler lack content.
• Outlook's own search shows the same gap (about 480 results on B vs 59 on A).

WHAT WAS TRIED (no change in the full-text count)

• Full index rebuilds, several times
• New Outlook profile; re-copying all PSTs, which triggered a full mail reindex (no event 10024 during mail indexing; little NPU activity; still 15)
• scanpst on all PSTs
• Outlook add-ins disabled; no third-party antivirus or iFilters
• PDF set to properties-only to rule out the PDF filter, later restored
• Outlook search options, Indexing Options and the Outlook search registry key compared across PCs: differences were file paths only, apart from the .ost entry below
• File Types: .pst and .msg identical on both PCs. .ost was set to the Plain Text filter with contents on PC A and to properties-only on PC B. Setting PC A to match PC B and rebuilding made no difference to the counts.
• [add if done: new Windows user account test; Online Repair of Microsoft 365]

OTHER OBSERVATIONS

• About 20 event 10024 (search filter host timeout) entries occurred while indexing local files (jpg, docx, pptx, msg, doc), none during mail indexing, so they don't appear related.
• Index queries in 32-bit PowerShell returned different, inconsistent email counts from 64-bit PowerShell.
• Exporting all email rows stopped with HRESULT 0x80041607 at one row on both PCs, so row totals are approximate. The counts above are unaffected.

EXPECTED

Both PCs return similar full-text results for the same mail.

ACTUAL

PC A's full-text index holds content for only a small fraction of mail items,

although the items and their properties are indexed.

REPRODUCTION

Not reproduced with synthetic data. On a Copilot+ PC and a non-NPU PC with the

same Windows build, attach the same large PSTs in classic Outlook, let

indexing finish, and compare the three queries above.

REQUEST

Please advise what in the mapi16 content path could account for this on the

Copilot+ PC, and which logs would help. I can supply diagnostics.