Microsoft Exchange Online is the email service provided by Microsoft. At the time of writing, the most current version is Exchange 2016. This version was designed with Office 365 in mind, specifically to support multiple tenants in each Exchange organization, with the required logical separation and security controls in place.

The main function of Exchange is to provide a robust and secure email platform that can be used to communicate, make appointments, manage tasks, and organize emails in inboxes.

Exchange server is an enterprise class server that was first launched in 1996 and is currently the most widely-used email system in organizations. It provides a rich set of features such as:

• Routing and transport rules
• Encrypted and secure mail
• In-place hold that allows you to retain emails forever
• eDiscovery features to search for specific content throughout the whole organization

Microsoft Exchange Online is divided into three main workloads, depending on where the mail is stored and what the destination is:

• Exchange Online Protection (EOP): It is a Microsoft service that protects the Exchange platform from malware and spam.
• Exchange Online: Exchange Online is the main component of the Exchange platform and where the user data resides.
• Exchange Online Archive: It is a system that is used for archiving the email that is not needed in an offline device. Some plans have an unlimited storage quota.

The following diagram shows how email messages go through each of the Exchange platform components:

When Office 365 first receives an email, it goes through EOP and the message hygiene is analyzed; a set of algorithms are run to detect whether the message is safe to be delivered to its destination. After the email has passed through EOP, it goes to the Exchange Online mailbox, where you normally work with your inbox and folders. The last service is the archive, which is the part of the platform that handles old emails as a secondary mailbox.

In Exchange Online, you can choose from two separate plans, Plan 1 and Plan 2. The main differences between these plans are as follows:

It is possible, in the same tenant, to have different subscriptions and combine the products needed for each organization to accommodate its needs at any point in time. However, each user can only be assigned one plan for each workload.

When you remove a license, the data is removed, and you have 30 days to recover it, if it was a mistake. Unless the data is under a legal hold, after 30 days of being deleted, it will no longer be recoverable.