Configure POP and IMAP in Exchange 2007

The Internet is a fascinating mix of old and new technologies. For every new application or protocol such as Asynchronous JavaScript and XML (AJAX), an old technology is quietly soldiering on in the background. SMTP is a great example. I doubt SMTP's designers ever envisioned how prevalent and important it would become when they invented it more than 30 years ago, but it's still a crucial part of every major messaging system, and Exchange 2007 provides excellent support for it. Likewise, POP and IMAP are still widely used to provide message access to a variety of clients, including Microsoft Office Outlook, Outlook Express, Windows Live Mail, Microsoft Entourage, Apple Mail, and smartphones running Microsoft Windows Mobile software, Palm OS, and Symbian OS (to say nothing of dozens of lesser-known clients for various OSs.)

Exchange has supported IMAP and POP since Exchange 5.5. The way that support is implemented has changed greatly over time, and the way you manage and configure the protocols has changed too. The RTM version of the Exchange 2007 Management Console doesn't include support for managing POP and IMAP implementations. In Exchange 2007, you can still support IMAP and POP, but to do so you'll have to master the Exchange Management Shell.

POP and IMAP Explained
If you're used to supporting rich Messaging API (MAPI), WWW Distributed Authoring and Versioning (WebDAV), or Exchange ActiveSync clients, you might not be familiar with IMAP and POP. Both are fairly simple protocols, and they share some similarities. However, they have some significant differences from each other and from other protocols you might be used to working with.

POP is by far the simpler of the two protocols; it supports reading, downloading, and deleting messages in a single inbox folder, along with setting a few properties (e.g., the read and unread status of a message). POP doesn't support multiple folders, moving messages, search, rules, or most other semi-modern mail-client features. For that reason, almost all POP clients create a local cache of messages and perform operations against it. This leads to a common problem in which a user reports that messages are disappearing; the problem happens when you leave a POP client running and set it to download messages then delete them. When new messages come in, they end up in the POP client's local mailbox instead of on the mail server, so they seem to have disappeared. This problem is exacerbated if you use POP on multiple machines because messages can become scattered across the machines.

POP is typically carried over TCP port 110, whereas IMAP uses TCP port 143. Both protocols can (and should) be secured with SSL, in which case POP uses port 995 and IMAP uses port 993. The Exchange implementation of both protocols supports several authentication methods, including plain credentials and GSSAPI, which can be used for Kerberos-based logons.

Get Started
As in earlier Exchange versions, IMAP and POP services in Exchange 2007 are provided by two Windows services. The Microsoft Exchange IMAP4 service (whose short name is MSExchangeIMAP4) and Microsoft Exchange POP3 service (MSExchangePOP3) are installed by default, but they're turned off, and their service state is set to manual. Before you can provide POP or IMAP access to your users, you have to start the service you need and set its service startup state to automatic. You can easily do this through the Services console in Windows, but it's just as easy to do it with the Exchange Management Shell, and I recommend that you give it a try. The commands are simple: Start-service MSExchangeIMAP4 will start the service, and Set-Service MSExchangeIMAP4 –startupType automatic will set the startup type.

Why do I recommend using Exchange Management Shell? Because you'll need to use it to manage all of the other settings for the services, and starting and stopping services is a safe way to practice. There's no provision in the release version of the Exchange Management Console for managing the settings on these services, so if you're going to use them you'll have to get familiar with the Get-IMAPSettings and Set-IMAPSettings Exchange Management Shell commands (and their POP equivalents). You'll need to use these tasks to make any sort of change to the IMAP and POP settings. Microsoft has announced that the Exchange Management Console will support a graphical interface for managing POP and IMAP settings when Exchange 2007 SP1 releases, but that won't be until sometime in late 2007.

However, you might find that you don't need to do much. When you install Exchange 2007, it generates a self-signed certificate that you can use to secure your network traffic with Secure Sockets Layer (SSL). By default, this certificate will be assigned to the IMAP and POP services, and those services will automatically use it, which means you'll have to use IMAP and POP clients that are compatible with self-signed certificates. The most common customization for Exchange 2007 IMAP and POP servers is replacing these default certificates with certificates issued by third-party Certificate Authorities (CAs).

Replace the Default Certificates
To modify the certificates assigned for use with Exchange services, you have to use the Enable-ExchangeCertificate task in Exchange Management Shell. Once you've obtained the certificate you want to use, you must install it on the Exchange 2007 client access server where you'll be using it. The installation steps will vary somewhat according to the CA you're using to issue the certificates. However, once you install the certificate, you'll need to view the certificate properties to get its thumbprint. The thumbprint uniquely identifies each certificate on the system; you can think of it like a GUID. Here's what to do:

1. Log on to the Exchange 2007 client access server through an account that has administrative privileges.
2. Launch Microsoft Management Console (mmc .exe).
3. Select File, Add/Remove Snap-in; in the Add/ Remove Snap-in dialog box, click Add.
4. Select the Certificates snap-in and click Add.
5. Select Computer account, then click Next.
6. Select Local computer (the computer this console is running on), and click Finish.
7. Expand the Certificates (Local Computer) node, then the Personal node, then the Certificates node.
8. Select the certificate you want to use from the right-hand pane, right-click it, and choose the Properties command.
9. Click the Details tab.
10. Scroll down to the bottom of the properties list, where you'll see the thumbprint listed.
11. Select Thumbprint from the list, then select and copy the thumbprint when it appears in the text box.
12. Click OK.

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