Outlook OST corrupt error

We've been troubleshooting .ost corruption issues on desktops and laptops, Win 8.1 and 10, and Outlook via Office 365 going back almost 2 years to present. We've dug into countless areas, opened tickets with Microsoft, logged everything imaginable and we cannot determine the root cause. One of the only consistencies for us is that all laptops and desktops are running Sophos Endpoint, recently upgrading and enabling Intercept X.

Today, I just happened to stumble upon this post (and a few others) and decided to add a global exclusion in our Sophos configuration for *.ost to see if this makes any difference. It could be that Sophos is entirely unrelated, but this issue has impacted probably a dozen users anywhere from once every few weeks to a couple of times per year.

Yes, it's largely an annoyance as we just delete the .ost and let Outlook recache, but for some folks with very large mailboxes (and who like to have as much offline as possible), it can take a day+ to re-cache their mailboxes.

Yeah you can add the wild card on your exclusion and observe if there’s n improvement. 

Update: We made this wildcard change last week and over the weekend we had another instance of a user .ost corruption, so it doesn't seem like Sophos is related.

Thank you for your confirmation, have you tried reducing the size of the OST file by archiving them as PST? let say, you'll try advising users to always archive their mails every after 3-5 GB OST size. You may also perform a cleanup of their OST there might be lots of deleted emails residing on a deleted folder which adds the size of the OST file. 

I did raise the support ticket with Sophos and Installed latest hotfix Current Hotfix Version: 3.8.2.292 yesterday. We are monitoring the clients machine for past 24 hours no issues reported. 

I did raise the support ticket with Sophos and Installed latest hotfix Current Hotfix Version: 3.8.2.292 yesterday. We are monitoring the clients machine for past 24 hours no issues reported.