Exchange Center

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.

Many companies use old-style public folders, known as legacy public folders, on Exchange Server 2010. Often, the public folder hierarchical structures have grown uncontrollably for years. And not only in terms of data volume but also in the number of folders and the folder depth in the public folder hierarchy. For these reasons, many companies fear legacy public folder migration to modern public folders.

On July 24, 2018, the Exchange Product Group released the preview version of Exchange Server 2019. This version is the third version of modern Exchange Server. Like the previous versions, Exchange Server 2019 benefits from the product developments tested and implemented in Exchange Online. But not all features available in Exchange Online are available in the on-premises version of Exchange Server. Additionally, not all features that are announced for the new release will be available when the RTM build is released. That is something that we have learned with previous releases of the product.