This tip is really a general Mail tip that isn't specific to the Mac, but I'm sure many mac users have had the experience of their mail client chopping off the end of long URLs. When this happens, the person who received the message containing the URL can't click on it to go to the web page.

An easy way to avoid this is to put your URL in when sending it. When the person you are sending it to receives the email, the URL will still be nice and click-able.