From November 1, 2021, Microsoft requires Outlook 2013 Service Pack 1 (with fixes) as the minimum client version to connect to Exchange Online. Given all the publicity about attacks against the on-premises version of Exchange earlier this year, it's a wonder why organizations continue to allow people to use outdated client software to connect to Exchange Online. In any case, the drop-dead date is November 1. If you have any old Outlook 2007, Outlook 2010, or Outlook 2013 (before SP1) clients, it's time to start upgrading.
When Exchange Server 2010 is first installed many administrators encounter an issue with Outlook clients and SSL certificate warnings, relating to the Autodiscover service and the use of SSL for Exchange Server 2010 by default.
Microsoft has released an update for Office 2007 that adds support for Exchange Server 2010 Personal Archives. However there are still a few limitations to be aware of.
When an Outlook 2010 user tries to open more than 30 calendars simultaneously they may receive an error that no more calendars can be opened.