For some weeks now, we encounter performance issues with certain Shared mailboxes.
When browsing into the shared mailbox, Outlook Client freezes from time to time. Seems to have lost connection with Exchange Online as we receive on-screen notifications that Outlook is trying to receive data from the exchange sercer. We disabled the cache, disabled ipv6, disabled hardware acceleration,.... but nothing seems to help. The mailbox only have a usage of 30GB from the 50GB that is available.
It's not with every shared mailbox we have.
Does anyone know where this comes from? I was thinking about maximum number of delegates, the mailboxes that encounters this problems have 20+ delegates. Is there a limitation?
Only is a relative term :) 30 GB is a large size for a mailbox, especially one being accessed in sub-optimal scenarios, which is often the case with shared mailboxes. I would strongly suggest trying to bring the size down, or switch to using OWA instead of Outlook to access the shared mailbox.
And yes, the 20+ delegates also contributes. Especially if all of them have added it to their Outlook profiles. Remove any automapping, remove it from Outlook even and have them access it only on demand, via OWA preferably.