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.
Exchange Online protocol authentication policies control what protocols a user can connect to mailboxes with, but it would be much better if we didn’t have to worry about some old and insecure protocols. Azure Active Directory gives Office 365 tenants the chance to clamp down on IMAP4 and POP3 connections and close off some of the holes that attackers try to exploit. Microsoft says that this can lead to a 67% reduction in account compromises, so that’s a good thing.