The Desire HD and Desire Z feature HTC's own Exchange email client, distinct from the native Android client. When launching the Mail application on the Home screen for the first time, you will be prompted to specify what type of email account you want to create:

Select Microsoft Exchange ActiveSync:

Enter in your email address and password, the same password you use to log into your office PC, and tap Next. The device will attempt to determine the settings of your email account automatically based on the email address entered. If your Exchange server uses a self-signed certificate, you may be warned that the identity of the certificate cannot be guaranteed:

Tap Continue

If the device is not able to determine all of the settings to use automatically, you will be prompted to enter them manually.

Complete the server address - if you don't know this information contact your IT department, but if you access your email via a web browser, then it will be this address - normally in the form mail.mycompany.com

Enter in your domain information, again this can be found out from your IT department, but is normally the same as the contents of the "Log Into" field on your PC when you log in, under the Username and Password fields

Verify that the username has been determined correctly.

Specify whether or not the connection requires SSL - if you don't know, but you do access your email via a web browser, then if the web address contains "https" at the start then your connection does use SSL.

Once all of the settings have been entered, tap Next

Specify which mailbox folders you want to synchronise and how often you want new mails to arrive on the device. Tap Next

Enter in a name for the account to identify it, and tap Finish.

Your device is now configured and email will now synchronise to the device.

NOTE - on the Desire HD it is possible to add multiple Exchange email accounts rather than just one, simply run through the above procedure again to add the second account.

Within the Inbox, all mail folders can be viewed by selecting Folders from the menu:

In the Settings menu you can further customise how mail is delivered, and how much of it, including attachment size limits:

as well as define synchronisation schedule settings, specifying the hours of the day you want mail to be pushed, and the hours that you want to check mail manually or have it synced on a schedule:

You can configure how the arrival of new mail is alerted:

and within Settings --> Accounts & Sync you can adjust which mailbox folders are synced:

as well as how far back into the past you want to synchronise calendar information: