We have a major issue with office 365 performance for secretaries and user who use multiple calendars and large mailbox:
When user use multiple calendars and sync few mailboxes the performance is very poor and sometimes the outlook freeze and crash, we tried to work with Microsoft few times in the past also to set offcut and to investigate this issue currently with no luck, almost everything already execute including power shell permission check remove and add, add -in remove, change outlooks versions, updates, new computers, new installations, different locations, different networks, etc.
We need a solution ASAP since this issue occur in few of companies that we support and Microsoft has not deliver solution yet almost 9 months that we open tickets and work with Microsoft support regarding this issue.
1. Is it possible to define quality of service to Microsoft Office 365?
2. Is it possible to allocate more resources on exchange office 365 in order to troubleshoot this problem?
3. Is there any other option like proxy or third party software that could resolve this performance issue for users who use large mailbox and multiple calendars?
All the companies that worked on local exchange before migrate to 365 worked without any problems, also some worked on remote exchange located in different country