Exchange Center

Exchange Hybrid environments have come of age. What was once considered a transitional, temporary solution on the path to Microsoft 365 just a few years ago has become a permanent configuration for many organizations. It offers flexibility, control, and a fair share of complexity. This very complexity often leads to a common issue: visibility gaps. In simple terms, it means you are unaware of what you don’t see.

What a year we have had! Who would have thought at the beginning of 2025 that Exchange administrators would be sweating so much? Even though much of it could have been avoided.

Centralized Mail Flow (also known as Centralized Mail Transport, CMT) is an option in Exchange hybrid environments whereby all outgoing Internet messages from mailboxes in Exchange Online are first routed through the local Exchange organization before being delivered to the Internet. Similarly, depending on the MX strategy, incoming Internet messages can first pass through the local environment before being delivered to cloud mailboxes. The goal is usually to continue applying central compliance, DLP, encryption, journaling, or gateway functions in the local infrastructure. As a rule, CMT is configured as part of the hybrid configuration using the Hybrid Configuration Wizard (HCW).

Microsoft is changing how hybrid authentication works between on-premises Exchange servers and Exchange Online. The long-standing Shared Service Principal (“Office 365 Exchange Online”, App ID 00000002-0000-0ff1-ce00-000000000000) will no longer be supported. Each tenant must deploy a dedicated Entra enterprise application by October 31, 2025. 

Why You Must Upgrade to Exchange Server SE Before October 2025

Microsoft is ending support for Exchange Server 2016 and 2019 on October 14, 2025, making it essential for IT teams to upgrade to Exchange Server Subscription Edition (SE) to maintain security and compliance.

Next year, Exchange Server will turn 30, a remarkable milestone for a platform that was often prematurely declared obsolete. The fact is: email remains an indispensable means of communication. According to CloudHQ's Email Statistics report, the number of global email accounts is expected to rise from approximately 4.8 billion today to over 5.6 billion in the next few years. Today, over 392 billion emails are sent daily, and by 2030, this number is expected to grow to over 500 billion. So, the question is not whether email will remain relevant.  

Exchange Server has two core components. First, there is the mailbox component, with all the required client access protocols and well-known mailbox functions. The second major component is the message flow, with receiving, processing, and sending email messages.

Before we talk about Exchange Server's Managed Availability features, let's first remember the architecture of Exchange Server.

Since the early days of Exchange Server, the limits of user mailboxes were strictly regulated. In many Exchange organizations, these quota limits were configured on a mailbox database level and were therefore consistent for all mailboxes stored in the same database. This approach was selected because the existing hard disk space was scarce and expensive in the past.

The virtualized operation of Exchange Server has been a hot topic for discussion ever since the introduction of hypervisor platforms. Often these discussions are very emotional, and the valid arguments rarely heard.