Every Exchange Online tenant has four mailbox plans. Exchange uses the plans to populate some important mailbox settings based on the license assigned to the mailbox owner. This article explains the four mailbox plans, how to update the plan settings, and some of the things you can’t do with mailbox plans. We also include some PowerShell to report the mailbox plans assigned to users in your Office 365 tenant.
Despite the age of the protocols, you can cheerfully connect a wide range of IMAP4 and POP3 clients to Exchange Online. If you do, you might need to consider how to handle calendar appointments, and if you want to use iCAL, you’ll need to make some adjustments with PowerShell.
A recent update for Exchange Online gives extra control over who can access public folders. The change is intended to help with scalability, but it can be used to turn public folders off for any mailbox for which you care to disable access.