Applies to: Exchange Server 2007 SP3, Exchange Server 2007 SP2, Exchange Server 2007 SP1
Topic Last Modified: 2008-04-29

This topic provides basic information about client connectivity to Microsoft Exchange Server 2007 through Post Office Protocol version 3 (POP3) or Internet Message Access Protocol version 4rev1 (IMAP4). By default, users who have mailboxes on computers that are running Exchange 2007 can access their mailboxes by using Microsoft Outlook, or Office Outlook Web Access, Microsoft Exchange ActiveSync, or Outlook Voice Access. Outlook, Office Outlook Web Access, and Outlook Voice Access enable your e-mail users to use the comprehensive set of features that are available to clients who have mailboxes on computers that are running Exchange 2007.

POP3 or IMAP4 cannot be used to send messages from a client application to the e-mail server. E-mail applications that use POP3 and IMAP4 to send messages rely on the SMTP protocol for the sending of messages. The connector for receiving e-mail submissions from client applications that use POP3 or IMAP4 is created automatically on every Hub Transport server. For more information about connectors, see Receive Connectors.

POP3 is a frequently used e-mail Internet protocol. By default, when POP3 e-mail applications download e-mail messages to a client computer, the downloaded messages are removed from the server. So when a copy of your user's e-mail is not kept on the e-mail server, the user cannot access the same e-mail messages from multiple computers. However, some POP3 e-mail applications can be configured to keep copies of the messages on the server so that the same e-mail messages can be accessed from another computer. POP3 client applications can only be used to download messages from the e-mail server to a single folder (usually the Inbox) on the client computer. The POP3 protocol cannot synchronize multiple folders on the e-mail server with multiple folders on the client computer. POP3 also does not support public folder access.

E-mail client applications that use IMAP4 are more flexible and generally offer more features than e-mail client applications that use POP3. By default, when IMAP4 e-mail applications download e-mail messages to a client computer, a copy of downloaded messages remains on the e-mail server. Because a copy of the user’s e-mail message is kept on the e-mail server, the user can access the same e-mail message from multiple computers. With IMAP4 e-mail, the user can access and create multiple e-mail folders on the e-mail server. Users can then access any of their messages on the server from computers in multiple locations. For example, most IMAP4 applications can be configured to keep a copy of a user's sent items on the server so that they can view their sent items from any other computer. IMAP4 supports additional features that are supported by most IMAP4 applications. For example, some IMAP4 applications include a feature that lets the user view only the headers of their e-mail messages on the server—who the message is from and the subject—and then download only the messages that they want to read. IMAP4 also supports public folder access.

Send Receive Options for POP3 and IMAP4 E-Mail Applications

POP3 and IMAP4 e-mail applications let users choose when they want to connect to the server to send and receive e-mail. This section discusses some of the most common connectivity options and also provides some factors your users should consider when they select connection options available in their POP3 and IMAP4 e-mail applications.

Common Configuration Settings

Three of the most common connection settings that can be set on the POP3 or IMAP4 client application are:

  • To send and receive messages every time that you start the e-mail application. When this option is used, mail is only sent and received upon starting the e-mail application.

  • To send and receive messages manually. When this option is used, messages are only sent and received when the user clicks a "send and receive" option in the client user interface.

  • To send and receive messages every set number of minutes. When this option is used, the client application connects to the server every set number of minutes to send messages and download any new messages.

For information about how to configure these settings for the e-mail application that you use, see the Help documentation that is provided with the respective e-mail application.

Considerations When Selecting Send Receive Options

If the device or computer that is running the POP3 or IMAP4 e-mail application is always connected to the Internet, the user may want to configure their e-mail application to send an receive messages every set number of minutes. Connecting to the server at frequent intervals lets the user keep their e-mail application up-to-date with the most current information on the server. However, if the device or computer that is running the POP3 or IMAP4 e-mail application is not always connected to the Internet (for example, if the user connects to the Internet by using a dial-up connection), the user may want to configure the e-mail application to send and receive messages manually. In a dial-up connectivity scenario, sending and receiving messages manually can potentially reduce the time that a user is connected to the Internet.

If the user is using an IMAP4-compliant e-mail application that supports the IMAP4 IDLE command, the user may be able to send e-mail to and receive e-mail from their Exchange mailbox in near real time. For this connection method to work, both the e-mail server application and the client application must support the IMAP4 IDLE command. In most cases, users do not have to configure any settings in their IMAP4 application to use this connection method. 

POP3 and IMAP4 Applications

Because Exchange 2007 supports POP3 and IMAP4, users can use many POP3 and IMAP4 client applications to connect to Exchange 2007. These applications include Outlook, Windows Mail, Outlook Express, Entourage and third-party clients such as Mozilla Thunderbird, and Eudora. The features supported by each e-mail client applications vary. For information about the specific features offered by specific POP3 and IMAP4 client applications, see the documentation that is included with each application.

For More Information

For the steps that users must follow to connect to their Exchange 2007 mailbox by using the POP3 or IMAP4 protocol, see How to Connect to an Exchange Mailbox by Using POP3 or IMAP4.

For information about how to verify that your Exchange environment is configured to support POP3 or IMAP4 connectivity, Verify that Your Exchange Environment is Configured to Support POP3 and IMAP4.

For more information about how to manage POP3 and IMAP4 in Exchange 2007, see Managing POP3 and IMAP4