Exchange Online has different ways to provision mailboxes. Exchange Online is a standard service within Microsoft 365, which in the simplest case provides a mailbox. However, an Exchange Online mailbox also serves as a storage location for user-related data from other Microsoft 365 services. The most prominent example of this is Microsoft Teams. What exactly happens when Exchange Online provisions a mailbox depends on different factors. Especially when using hybrid identities synchronized with Azure AD Connect, there are essential points to consider.
M365 - Exchange Online Center
ENow Software's Microsoft Exchange Online blog built by Microsoft MVPs for IT/Sys Admins.
When users report to IT support that Exchange Online delivers email messages to the Junk Email folder of their mailbox incorrectly, the reason is often a misconfiguration of Exchange Online Protection settings. Such a situation mainly affects Exchange Hybrid configurations that use the centralized message flow.
Exchange Web Services (EWS) have been an integral part of Exchange since Exchange Server 2007. They are used not only by Exchange Server and Exchange Online for communication between Exchange Servers and as part of hybrid communication. Email clients also use web services. EWS is a SOAP-based API, but in the meantime, there are more modern protocols. Back in 2018, the Exchange product group announced that there would be no further development for the EWS protocol in Exchange Online. Indirectly, the EWS Managed API README-file on GitHub contains an announcement for Exchange Server.
Customizing and configuring an Exchange organization has been a daily task for Exchange administrators for years. In a local Exchange organization, you can customize mostly anything you like. There is no requirement for enabling the organization for customization. But in Exchange Online, the situation is different.
Why Modern Exchange Hybrid?
The question of why should I implement Exchange Modern Hybrid is justified. Exchange Modern Hybrid is specially designed to simplify implementing Exchange Hybrid Mode by eliminating the requirement for inbound HTTPS connections to an on-premises Exchange organization. The technical specifications for Classic Exchange Hybrid are sometimes unsuitable for enterprises. You can read more about the differences between the two Exchange Hybrid modes in ENow's blog post, "What are your Hybrid Options."
Deactivation of Basic Authentication in Exchange Online
In their blog article, "Improving Security - Together," the Exchange product group announced that the insecure Basic Authentication authentication method switches off on October 13, 2020, not just for Exchange Web Services (EWS), but also for Exchange ActiveSync (EAS), POP, IMAP, and Remote PowerShell.
With the use of the Office 365 platform, application monitoring requirements have changed. In your on-premises IT infrastructure, you normally monitor the availability of applications by solely checking server reachability. In some cases, you might choose to implement enhanced application monitoring by accessing dedicated protocol endpoints.