Sure! You can set up most desktop email programs to route your emails through Mandrill by specifying Mandrill as the outgoing server.  Below we'll walk through some common programs you might use:

Outlook

Thunderbird

Mac Mail

Outlook

Here's how to set up Mandrill as the outgoing server in Outlook. Things may look slightly different if you have a different version of Outlook.

1. Click the File menu, and then Account Settings > Account settings.
   
2. Select an account that is already set up, and then Change... to modify the outgoing settings for that account. If you're setting up for the first time, select New... and then Manually configure server settings or additional server types. Choose Internet E-mail.
   
3. Fill in your name and email address for the user information if they aren't already provided (if you're changing an existing account, these should already be filled in).
4. Set the outgoing mail server (SMTP) to smtp.mandrillapp.com. The login details at the bottom should correspond to your incoming email server.
   
5. Click More Settings... and then choose the Outgoing Server tab.
6. Make sure the check box My outgoing server (SMTP) requires authentication is checked.
7. Select the radio button for Log on using and provide your Mandrill username and a valid API key for your account.
   
8. Click Ok to save your changes.
9. Click Next > or Test Account Settings... If you test the account settings, you shouldn't get any errors. If you do, check that the ingoing and outgoing servers are correct or get more details about the errors so they can be resolved.
10. Click Close to close the window with the test results.
    
11. If you were setting up a completely new account, click Finish to complete the new account wizard.
    

Thunderbird

Mac Mail

If you already use Mac Mail with the email address you want to send "from", you'll just need to set up a new outgoing server to use.

1. Go to the Mail Preferences and make sure you're on the Accounts pane.
   
2. In the Outgoing Mail Server (SMTP) drop down, choose Edit SMTP Server List...
   
3. Click the + button to add a new SMTP server.
   
4. Provide a description and the server name. The server name should be smtp.mandrillapp.com.
   
5. Click Advancedto provide additional details.
   1. Use the default ports if you don't want to encrypt the connection.
   2. If you do want to encrypt the connection select the option to Use Custom port: and specify port 587 and check the box to Use Secure Sockets Layer (SSL).
   3. Make sure the Authentication is set to Password.
   4. Your Mandrill username is the User Name, and the Password is any valid API key for your Mandrill account.
      
   5. Click Ok to save the changes.
6. If you want to send through Mandrill by default, choose the new Mandrill SMTP option that you set up in the Outgoing Mail Server (SMTP) drop down.
   
7. If you want to send only through Mandrill, check the box next to Use only this server.
   

Create a new email to send through Mandrill if you want to test your settings.  If you didn't set Mandrill to be the only outgoing server, make sure you choose the Mandrill option to send from.