An email address identifies the account that messages should be delivered (e.g., firstname.lastname@example.org). An account can have multiple email addresses. Each account in Microsoft 365 has only one primary address, but an account can have multiple alternate addresses. An account will accept email for any email address on the account.
In email addresses, the domain is the part of an email address comes after the @ symbol. For example, for the email address of "email@example.com", the domain is "wisc.edu".
Exchange ActiveSync Protocol
Exchange ActiveSync (also known as EAS) is a communications protocol designed for the synchronization of email, contacts, calendar, tasks, and notes from a messaging server to a smartphone or other mobile devices. The protocol also provides mobile device management and policy controls.
A service -- similar to IMAP, POP3, and ActiveSync -- that works to transfer and synchronize email/calendar information between the server and the end user's client.