Outlook - search problem

Question

I would like to ask you for advice regarding a certain situation, if somebody have had similar experiences. We have a colleague who has a very large number of emails in Outlook (Inbox – over 45 GB, Online Archive – over 80 GB, additional archives – over 100 GB), which makes searching difficult (Outlook often cannot find the requested email based on the given criteria). Unfortunately, due to the nature of the work, all of these emails are necessary for uninterrupted operation. We have considered the idea of moving part of the archive to another application [Moderator note: third-party tools] so that these archives could be used when needed. However, the issue is that these applications are not Microsoft products, which raises concerns about the security aspect, and additionally, they have not proven to be particularly efficient when it comes to email search. Thank you in advance for your response.

Answer 1

Hi Dragan Krsmanović

You are right to consider about the security risks. These third-party tools are not controlled by Microsoft, and Microsoft cannot make any representations regarding the quality, safety, or suitability of any software. So, it is not recommended to use third-party software.

You mentioned you had some additional archives – over 100 GB, is it one big local .pst file or many .pst file. The limit size for .pst and .ost are 50 GB, if it exceeds the limit, it will reduce the performance. Configure Size Limit for PST and OST Files In Outlook | Microsoft Learn

If it is a local file, you can consider Enable auto-expanding archiving | Microsoft Learn (Available for E3, E5, Business Premium). This feature will enable additional storage space for archive mailboxes (up to 1.5 TB). You can move the local .pst file into the Online Archive.

You can consider using Outlook Web or New Outlook since they rely on server‑side search. The performance will be more consistent.

If you prefer Classic Outlook, you can store all emails offline by going to File > Account Settings > Change > Set the slider to all right. This will keep all emails offline and might return more accurate results. This only apply for primary mailbox; it does not download full emails for Online Archive.

---

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

Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.