Mobile access in Exchange Online

Your users can access their Office 365 mailbox from a wide variety of devices: mobile phones, tablets, laptops, and even devices such as e-readers. These devices can use Exchange ActiveSync, POP3, or IMAP4 to access Office 365 mailbox data.

Exchange ActiveSync

Exchange ActiveSync is a synchronization protocol that's optimized to work together with high-latency and low-bandwidth networks. The protocol, based on HTTP and XML, lets mobile phones access an organization's information on a server that's running Microsoft Exchange. Exchange ActiveSync enables mobile phone users to access their email, calendar, contacts, and tasks, and to continue to access this information while they're working offline.

Exchange ActiveSync provides the following:

  • Support for HTML messages

  • Support for follow-up flags

  • Conversation grouping of email messages

  • Ability to synchronize or not synchronize an entire conversation

  • Support for viewing message reply status

  • Support for fast message retrieval

  • Meeting attendee information

  • Enhanced Exchange Search

  • PIN reset

  • Enhanced device security through password policies

  • Autodiscover for over-the-air provisioning

  • Support for setting automatic replies when users are away, on vacation, or out of the office

  • Support for task synchronization

  • Direct Push

  • Support for availability information for contacts


POP3 was designed to support offline mail processing. With POP3, email messages are removed from the server and stored on the local POP3 client unless the client has been set to leave mail on the server. This puts the data management and security responsibility in the hands of the user. POP3 doesn't offer advanced collaboration features such as calendaring, contacts, and tasks.


IMAP4 offers offline and online access but, like POP3, IMAP4 doesn't offer advanced collaboration features such as calendaring, contacts, and tasks.