A Preferred Architecture (PA) Exchange deployment would include four Exchange servers distributed across two separate AD sites. Incoming, outgoing, saved, drafts, calendars–everything is done through Microsoft Exchange and stored on the server. To download updates, your computer needs to be able to access the Internet and to establish a connection on TCP port 80 (HTTP). The mailbox server components of Exchange rely on database availability groups (The DAG is the fundamental Exchange subsystem for ensuring HA. The concept of Quorum is the idea that, in the event of a failure of some DAG members, there are rules to govern what resources the remaining members can provide. These lists are not intended to be definitive.The most common choice for businesses looking for a messaging solution will be between Exchange on-premises and Exchange Online.Microsoft offers Exchange as a SaaS offering called Exchange Online. Get to know third-party offerings and explore the advantages...Learn the basics of cloud computing with answers to these frequently asked questions. A hybrid deployment allows an organization to retain some control and use some of its on-premises functionality, such as secure mail transport, with a cloud-based mailbox.Organizations can also use cloud-only deployments that put all the mailboxes in a Microsoft data center.Microsoft positions Exchange Online as one way to reduce the workload of an IT staff. These options, which included multiple ways to build a database cluster, ended up being complicated and confusing to deploy and maintain.Exchange 2010 was a minor release of Exchange Server. Doing so is not recommended in most circumstances and should only be done after direct consultation with Microsoft support.Datacenter Activation Coordination (DAC) mode is a feature of DAGs that is designed to prevent situations in which an outage causes two copies of a database to be live on two different servers. Exchange 2000 included an Instant Messaging feature that was later spun off to Office Communications Server. Many features and capabilities were first introduced in Office 365 before being delivered on-premises.

Below are some high-level pro and con comparisons. The job of a DAG is: (1) to ensure that there are multiple copies of each mailbox ready to be activated and (2) to accept client requests in case the active copy becomes unavailable. A network failure occurs in the link between the two data centers. DAC mode requires manual intervention when the server hosting the database cannot reach a majority of the DAG member servers.Microsoft best practices call for DAC mode to be activated on any DAG that has two or more members and uses continual replication. There are open source versions of Zimbra available, which include different licensing options.All the different messaging solutions with different features and focuses make a straight pro and con comparison difficult. In addition to managing messaging traffic, Exchange Server provides several other collaboration features, like calendaring, and tight integration with other Microsoft Office applications.Exchange Server is known for its high availability (HA) features that ensure continued service in different outage scenarios. We are often asked the question, “Do we choose a Singapore or Australian host?” by companies when rolling out Exchange. These quorum rule sets exist to provide consistent operation of a DAG and act as a tiebreaker in situations where DAG nodes lose communication with each other.When a DAG has an even number of nodes, it uses Node & File Share Majority quorum mode. Get broad coverage across devices, apps, cloud services, and on-premises. When this happens, the two different copies of the database diverge, causing the potential loss of user data when the two different copies attempt to reconcile.In addition to preventing split-brain conditions, DAC mode enables DatabaseAvailabilityGroup cmdlets to be started, stopped and restored. The SAM is not responsible for selecting which copy of the database is activated after a failure. This was the first version of Exchange that could be run and managed with a GUI.