Here’s a list of features in Apple’s Mail application which I use regularly and people appreciate when I point them out.

1. Connection Doctor – Go to the Window menu and select Connection Doctor. A small separate window will appear. It quickly tests all of your incoming and outgoing connections to your mail servers. After a few seconds you should see green dots to the left of each item listed. If you see yellow or red dots then there’s a problem. If you’re having problem sending or receiving email, open Connection Doctor. It might give you some information that helps you figure out where the problem is. If you see green dots next to all items and you still can’t send a particular email message, then it’s time to look for typos in the recipient’s email address.
2. Send Again – To use this feature just click on a message in your Sent mail folder or any other mail folder, for that matter and then select Send Again from the Message menu. I use this feature when I want to send the same email message to different people but I want to address the message individually to each of them. This feature is also handy if I send a message and immediately remember that I forgot to include a piece of information. I’ll select the message I just sent from the Sent folder and add the missing information at the top of the message.
3. Remove Attachments – To use this feature select one or multiple messages and then select Remove Attachments from the Message menu. One can use this feature to quickly strip email messages of all attachments while preserving the message itself. This is useful for housekeeping purposes. Most people don’t need to hold onto the attachments for messages that they sent since that document is typically saved elsewhere on your hard drive.
4. QuickLook – This feature requires that you have Mac OS X version 10.5 or 10.6 installed. As you may know, QuickLook is feature of the Finder. Click on a file in the Finder and press the Space Bar key. OS X will show you a quick preview of the contents of the document without having to launch the application that created it. QuickLook doesn’t work with every type of document, but it works with the most common file types such as jpeg image, PDF and files made with Word, Excel, Pages or Numbers. Apple built QuickLook into Mail. If you have an email message with an attachment, look for the QuickLook button near the Attachments line of the email’s header information. It’s just a quick way to look at the attachment.