With the release of the Android 2.3 SDK it is possible to play with Google's support for the Exchange ActiveSync protocol which is included with the SDK emulator package.
It is important to note that just because the build of Android supports it, it is down to individual device manufacturers as to whether they choose to implement Exchange support at all, or may decide to develop their own client software.
This post is for geek interest only.

HTC and Motorola-based devices feature their own Exchange email clients.

For instructions on how to configure the Android SDK on MacOS, read this article - http://blog.brightpointuk.co.uk/running-android-sdk-mac-os-106-snow-leopard

Setting up the Exchange account

Launching the email client for the first time will prompt you to enter your email address and password:

You will then be prompted to specify the type of email account you want to set up:

The wizard will attempt to determine the correct settings to use automatically:

Should the wizard not be able to determine the settings to use, you will be prompted to enter the required configuration settings manually:

Your username will need to be entered in the form "domain\username"

These settings will be available from your IT department, but if you log into a Windows-based PC in the office, the domain information will be the same as that contained in the "Log Into" field when you press CTRL ALT DEL to access your PC (under the password field)
Your username and password will be the same as you usually use.

The Server Address will be the external name or IP address of your Exchange server. If you access Outlook Web Access via a web browser to check your mail, this will be normally be the same address, typically in the form "mail.company.com"

If your server requires a secure connection (you can tell if your Outlook Web Access URL uses https at the beginning, or redirects to an https address) then tick the option to use SSL.
If your Exchange server uses a self-signed, or non root-trusted SSL certificate, then tick the option to Accept all SSL certificates.

Provided that the client is able to successfully connect to the Exchange server based on the information provided, you can then specify how often you want mail to be checked, how far back into the past you want to sync, and what other mailbox folders you want to synchronise - contacts and calendar folders are supported:

You can then enter a name for the email account:

If your Exchange server uses security policies, you will be advised that these policies will be applied to your device and will be prompted to activate the policy:

Policies might include the ability to remotely hard reset the device or enforce a password on it without your involvement - this is presumably required to address the growing situation whereby devices used to access corporate resources are owned by the user rather than the company, and such agreements need to be made.

Once the account has been created, additional Exchange accounts can be configured by running through the same above procedure, Android 23 supporting multiple accounts.
Accounts can be viewed separately, or together using the Combined Inbox - accounts are colour-coded:

Once the account has been created, settings can be adjusted by accessing Account Settings from the menu:

Including such elements as your default signature as well as all the options configured during the initial setup

Mailbox subfolders can be accessed, but on my setup all folders were listed alphabetically, regardless of their location in the folder structure - if you have nested folders, these will all be listed alphabetically only one level deep.

When composing new email messages, contacts will be listed from the Global Address List automatically as you type:

You can also optionally assign different notification ring tones to different email accounts:

If you wish to review which security settings a remote email administrator can apply to your device, this information is accessible under Settings --> Location & Security Settings --> Device Administrators:

And administrators can be removed if desired:

Although doing so may also result in an inability to continue using the associated email account.

Visit the different manufacturers sections of the blog to view device specific Exchange support articles.