POP3 Clients and Exchange 

MS Exchange 2003, a powerful messaging solution, allows organizations to manage their messaging platform well. And when combined with Outlook 2003, this becomes the platform of choice for collaboration and groupware. However, at times you might want or need to access the services of Exchange, using one of the standard Internet mailing protocols, such as POP3 or IMAP4. You can, of course, connect from any mail client to Exchange 2003 via POP3 or IMAP4 and retrieve and respond to mail. But, there are other things that you can do with these protocols as well, when working with Exchange 2003,
something that is not possible with other mail servers. We'll see how you can use some of these services.

Enable calendaring for POP3 and IMAP4

An interesting feature of Exchange 2003 is Calendaring, where you can set a meeting request mail to anyone using Exchange. When the person receives it, he can Accept, Decline or 'Propose a new time' for the meeting request. If accepted, the meeting is automatically added to both, the sender and recipient(s) calendars. To use this functionality you require Outlook to be your mail client.

However, it is possible to perform the same action by using a combination of any other mail client (which supports POP3 or IMAP4) and OWA (Outlook Web Access). In this case, the meeting request mail is received on the mail client (such as Mozilla Thunderbird) and contains a URL. When you click on this URL, an OWA message window opens up that allows you to perform the same actions as mentioned above - Accept, Decline or 'Propose new time'.

To enable this feature, you need to first open System Manager > First Administrative Group > Servers > > Protocols. Now, right click on the POP3 protocol and select Properties. Go to the Calendaring tab and select the server where the meeting requests are downloaded. Normally you'd use the 'Use Recipient's Server' as the default server. If you do this, the URL that is sent to a recipient is of the following format:

http:///Exchange//Inbox/.eml

However, if your setup consists of a frontend server to receive requests, you will need to select the 'Use front-end server' option above. This will change the URL to the this format:

http:///Exchange//Inbox/.eml

You can also increase security by choosing to have SSL-based connections, by selecting the 'Use SSL Connections' option. This will make the above URLs work over HTTPS instead of HTTP.

Now, once this mail is received in the mail client, all the recipient needs to do is click on it. Certain mail clients, such as Outlook Express can render this within themselves and give their own interface for accepting or declining the request. Others will pop up a small Web dialog that will allow you to perform these actions. 

One important thing to note is that this technique will not work for POP3, in case, the mail client deletes the messages from the server, after downloading them. Messages must be kept on the server for this technique to work. IMAP4 does not have this problem.

Advanced IMAP4 settings for Exchange

IMAP4 is much more advanced than POP3 in terms of the features it offers. Exchange allows more functionality when using the IMAP4 protocol, than it does in the case of POP3.

The fast message retrieval option in IMAP allows clients to retrieve their e-mails much faster

One advantage is, when a mail client using IMAP4 requests the headers and information about a mail in a folder, Exchange can be set up to provide an estimate of the sizes rather than the actual sizes. This puts much less load on the server and provides faster response. To enable this setting, go to the Servers > > Virtual Server > Default IMAP4 Virtual Server > Properties. Then turn on the 'Fast Message Retrieval' option.

Another advantage is that, unlike POP3, which allows viewing and managing only the Inbox folder on the server, IMAP4 

allows retrieval and management of any set of mail folders from the server. This feature can be utilized to work with the Exchange Public folders. 

When an IMAP account is created on a mail client, ors the mail client requests a refresh of folders from the IMAP server (in this case, Exchange), a new folder list is created by the server for that user, and returned. Exchange has the ability to include all the Public folders accessible to that user to this list also. To enable this feature, go to the same default IMAP4 virtual properties dialog and turn the 'Include all public folders when a folder list is requested' option on. 

Now when a user requests a folder list from his mail client, using IMAP4, he will also get a list of Public folders on the Exchange server. He can start using them by posting to them or dropping items into them. 

As you can see, Outlook is not the only way that to gain access to some of the advanced features of Exchange 2003. Standard Internet mail protocols also allows some features.

Vinod Unny, Enterprise InfoTech