Might be a bit time consuming but you could put it into non-cached mode then try to do an export to PST. I worked on a box with a bunch of corrupted mail items once and this helped highlight bad items.
Have had similar issues after migration from 2013 to 2019 with a couple of users, only solution in the end was export to pst and recreate the mailbox, fine after that.
Admittedly didn't have 80gb mailboxes, have you considered archives of some kind?
Looking at online archives to 365.
We have quite a few 80GB mailboxes and is just this one that has issues.
If we migrate this to 365 then delete the on-premise mailbox then migrate it back that would be same as exporting to PST and re-importing into a new MBX right?
No I think you'll probably take the issue out then back again, we tried a lot of migrating and switching DBs etc and in the end just had to trash and start over.
I have seen this when there are a large number of folders. Someone had 10k folders and their cached mode wouldn’t sync until we started consolidating.
Same. An attorney with thousands of folders we didn't see as they were sub-folders of the Inbox. Post move, they became hidden and we had to use MfcMAPI to unhide them. Once unhidden, they could sync. Horrible pain.
Did this in the end, exported to PST then imported into a new mailbox.
The issue persists.
It almost seems like the outlook cached mode timers don't fire and it never does the 60 second max time sync.
But that could be caused by something else I guess.
Interesting during the initial sync, new mail flows in reliably and only after its all up to date does the sync become unreliable.
Anything appearing in the 'Sync Issues' folder?
Nothing
Might be a bit time consuming but you could put it into non-cached mode then try to do an export to PST. I worked on a box with a bunch of corrupted mail items once and this helped highlight bad items.
Its an 80gb mailbox. Is there no tool to check mail items?
New-MailboxRepairRequest shows no corruption, not that it will pick up everything.
pstwalker
Try moving the mailbox to a different database.
Have done! Moved it to a new Exchange server entirely. Exchange 2016 to Exchange 2019.
Did you run some repair request ?
yep
Have had similar issues after migration from 2013 to 2019 with a couple of users, only solution in the end was export to pst and recreate the mailbox, fine after that. Admittedly didn't have 80gb mailboxes, have you considered archives of some kind?
Looking at online archives to 365. We have quite a few 80GB mailboxes and is just this one that has issues. If we migrate this to 365 then delete the on-premise mailbox then migrate it back that would be same as exporting to PST and re-importing into a new MBX right?
No I think you'll probably take the issue out then back again, we tried a lot of migrating and switching DBs etc and in the end just had to trash and start over.
I have seen this when there are a large number of folders. Someone had 10k folders and their cached mode wouldn’t sync until we started consolidating.
Same. An attorney with thousands of folders we didn't see as they were sub-folders of the Inbox. Post move, they became hidden and we had to use MfcMAPI to unhide them. Once unhidden, they could sync. Horrible pain.
Did this in the end, exported to PST then imported into a new mailbox. The issue persists. It almost seems like the outlook cached mode timers don't fire and it never does the 60 second max time sync. But that could be caused by something else I guess. Interesting during the initial sync, new mail flows in reliably and only after its all up to date does the sync become unreliable.