Outlook (classic) on Windows 11: High search index workload

Question

Outlook (classic) on Windows 11: High search index workload

dark-rider 60

Hello,

after update from Windows 10 to 11, search indexer has changed in so far that Outlook (classic) repeatedly causes high search index workload. This was not the case with Windows 10.

First, when the search index is completed for user files and for Outlook, in my case it has 3.5 GB for 250.000 user files and 100.000 Outlook elements (.pst file of about 10 GB).

But then during daily work with Outlook, search index is reworked quite often (several times a day) and changes to 5.5, 7.5 or 9.5 GB and back - without reasonable data changes in Outlook.

The normal path to the search index files is:

C:\ProgramData\Microsoft\Search\Data\Applications\Windows

This regularly causes high search indexer workload (CPU) and changes much data (SSD) which among other things makes differential/incremental backups very large.

It seems that Outlook (classic) has a bug which causes this annoying behaviour - could you reproduce this and check + repair it?

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2 answers

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Answer 1

Chloe-V 13,450 Microsoft External Staff Moderator

Hi dark-rider,

Disabling Windows Search indexing for Outlook does not completely remove the ability to search, but it does affect performance, and the extent of the impact depends on several factors:

Slightly slower: For small mailboxes or recent emails, Outlook’s built-in search engine still works fairly well.
Significantly slower: For large PST files (such as your 10 GB file), older emails, or complex queries (e.g., by attachment type, sender, or date range), search can become noticeably slower and less accurate.

Microsoft has confirmed that search performance will be affected when Outlook is not indexed by Windows Search. Users may need to enter more precise queries (e.g., full email addresses or exact phrases) to get better results.

Therefore, it is true that search can be significantly slower, especially in enterprise environments or with large PST/OST files.

Thank you for your suggestion. I have noted your request to create an official support entry for this new bug, similar to the one published for the Outlook CPU issue a few months ago. I will forward this to the appropriate team for review and consideration.

Best Regards,

Chloe | Microsoft Q&A Support Specialist

dark-rider 60 Reputation points

2025-09-23T07:31:08.8233333+00:00

Dear Chloe-V,

I tested the suggested workaround, but when search indexer is deactivated for Outlook, searching in Outlook takes very long (several minutes up to many minutes) instead of only less than a second. So search will be unusable that way for most users (because most people will not use Outlook only for very small mailboxes).

I also checked the SSD wear, and this Outlook bug causing the search index being reorganized and rewritten several times a day in my case (with 10 GB .pst file) causes over 50 GB written per day.

So could you please register an official bug entry (to be listed also on https://support.microsoft.com/en-us/office/fixes-or-workarounds-for-recent-issues-in-classic-outlook-for-windows-ecf61305-f84f-4e13-bb73-95a214ac1230) to let this serious bug be fixed as soon as possible?
dark-rider 60 Reputation points

2025-10-05T10:24:29.02+00:00

Dear Chloe-V,

are there any news concerning this bug?
dark-rider 60 Reputation points

2025-10-24T05:29:18.23+00:00

Since Monday (October 20, 2025), the search index (Windows.db in C:\ProgramData\Microsoft\Search\Data\Applications\Windows) is suddenly no longer being rebuilt once or multiple times a day along with significant file size fluctuations.

Shortly before that, there was the monthly Windows 11 update, and version 2508 for Microsoft 365 in Monthly Enterprise Channel came. A possible connection to this is unclear (no specific mention of this in the release news).

I'll continue to monitor it, of course.
dark-rider 60 Reputation points

2025-11-09T12:23:58.5266667+00:00

Dear Chloe-V,

you confirmed the bug, but then nothing else can be heard from you - is this the regular "Microsoft way"?
dark-rider 60 Reputation points

2025-12-30T12:25:22.2333333+00:00

Further checking confirmed that after each update of M365 incl. Outlook (classic), so to 2508, to 2509 and to 2510, the bug disappeared for 5-10 days, but then it came back in the same way as before.

During these 5-10 days, Windows search was working fine as before incl. most current data, so the annoying reorganization of the search index after each restart of Windows or Outlook (classic) is not needed for proper function.

It's a pity that nearly no user will notice this severe bug because you can continue working during reorganization of the search index although it causes high CPU load and SSD wear, and Microsoft again as with similar bugs before does not do anything for many months now already.
Haytham-C 5,630 Reputation points Microsoft External Staff Moderator

2026-02-02T05:11:04.22+00:00

Hello dark-rider,
My apology for the late reply; as far as I know, we do not receive any information about this behavior(bug) as you describe above. I would advise submit your feedback via Microsoft Feedback and include as much detail as possible so the correct team can gather all information, in the meantime you can try the workaround that Chloe-v mention here.
Thank you for your understanding.
dark-rider 60 Reputation points

2026-02-02T08:22:56.1+00:00

I already also posted the bug on Microsoft Feedback:

https://feedbackportal.microsoft.com/feedback/idea/9e989cab-11fc-f011-bb46-7c1e529117fa
Chloe-V 13,450 Reputation points Microsoft External Staff Moderator

2026-02-03T06:16:17.9766667+00:00

Hi dark-rider,

Once submitted, it may take some time for your feedback to be reviewed.

Please note that this is a user‑to‑user support forum. Moderators and contributors, including external Microsoft employees, cannot directly intervene in Microsoft product features or access back‑end systems. Our role is limited to providing technical guidance and sharing information related to reported issues, requests, or ideas only.

Thank you for your understanding.
dark-rider 60 Reputation points

2026-02-03T08:19:09.21+00:00

Dear Chloe-V,

thank you for being back after such a long time!

On Sep 17, 2025 you wrote:

The issue reported is a bug in Outlook (classic) on Windows 11 related to the search indexer workload. ... I will continue monitoring this issue and inform you as soon as Microsoft provides an official fix.

So do you really know that Microsoft is working on this bug?
Chloe-V 13,450 Reputation points Microsoft External Staff Moderator

2026-02-03T13:22:56.8566667+00:00

Hi dark-rider,

Thank you for your message and for following this thread.

As forum moderators, our access to internal development and engineering details is limited. Our role is to support the community by sharing publicly available information and guiding users to the appropriate resources and official support channels.

At this time, I recommend that you regularly check and follow updates on the official Microsoft documentation and release notes pages, where confirmed fixes and product updates are communicated by Microsoft.

While I may not have access to deeper internal details, I will continue to support you within the scope of this community forum. Thank you for your understanding.
dark-rider 60 Reputation points

2026-02-04T05:17:47.0066667+00:00

Dear Chloe-V,

you did not answer my question: Do you really know that Microsoft is working on this bug, as you at least said on Sep 17, 2025 as quoted above?
Chloe-V 13,450 Reputation points Microsoft External Staff Moderator

2026-02-04T06:27:07.4+00:00

Hi dark-rider,

Thank you for the clarification, and I appreciate you raising this point.

I do not have access to backend tools or internal engineering status as stated above, so I’m unable to confirm whether Microsoft is actively working on or has already fixed this behavior. My role here is limited to sharing any information that Microsoft has publicly released.

Thank you for your time and understanding.
dark-rider 60 Reputation points

2026-02-04T08:38:24.0966667+00:00

So you're more or less a human FAQ repeater, what would be a pity for both me and you?

Chloe-V, so you lied on Sep 17, 2025! In my eyes, you should not do this job any more under these circumstances!

Answer 2

Hi dark-rider,

Thank you for posting to Microsoft Q&A Forum.

The issue reported is a bug in Outlook (classic) on Windows 11 related to the search indexer workload. This problem causes noticeable slowdowns in both Outlook and the overall system performance. It also contributes to SSD wear due to large and frequent write operations. Additionally, it inflates the size of incremental or differential backups unnecessarily, as backup software detects the constantly changing index files and treats them as modified data.

To resolve this, please try the following steps:

On your keyboard, press Windows + S (or click the Start button).
Type: Indexing Options > select the result that appears.
In the Indexing Options window, click Modify.
In the list of indexed locations, find and uncheck Microsoft Outlook.
Click OK, then Close to finish.

-> This will reduce CPU and disk usage, keeping your system more responsive.

-> You will still be able to search for emails in Outlook, but the search may be slightly slower than before.

I will continue monitoring this issue and inform you as soon as Microsoft provides an official fix.

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".

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dark-rider 60 Reputation points

2025-09-18T10:16:48.9566667+00:00

Dear Chloe-V,

thank you very much for your kind answer, for the temporary workaround and for initiating a bug fix!

-> You will still be able to search for emails in Outlook, but the search may be slightly slower than before.

Are you sure that searching in Outlook will be only slightly slower than with search indexing, or not maybe very much slower?

PS: Could you also create an official support entry for this new bug (like here for the Outlook CPU bug from some months ago)?