Outlook calendar shared not updating
The other shared mailboxes are fine, but they're only about 100-300MB each.
Once you've verified that your Internet connection is functioning properly, check that your account settings are properly configured.
I've never added a true Exchange Online shared mailbox as an additional account in Outlook, but this guy says it works just fine, including comments from 5 days ago indicating it's working: Bumping this thread because this just started happening with my Outlook 365 client.
I tried removing and re-adding the shared mailboxes but they still do not update - last emails received were 10th July.
7 people access another users mailbox which has 800 folders.
When they had mail on-prem I just turned off shared folder caching.
These can include Internet connectivity issues, inaccurate account information, glitches with the type of view you're using, and incorrect Auto Archive and Delegate Access settings.