Have you ever wanted to copy the header (To, From, Subject, etc.) and body from an e-mail in Mail? You can select the header area and copy it, and you can select the body area and copy it, but it doesn’t seem there’s any way to do both in one step. As it turns out, there is—at least, there is if you’re able to view the message in plain text mode.
View the message whose header and body you’d like to copy, then select View -> Message -> Plain Text Alternative. If you can’t select Plain Text Alternative, that means the e-mail was sent in HTML mode only, and you can’t use this trick. (You can view the message in Raw Source mode, but you’ll then have to edit the text substantially to make it readable after pasting.)
Once the message is in plain text mode, click and drag your selection—but start at the bottom of the text you’d like to copy, not at the top of the header area. Then drag up towards the top of the message, and you’ll see that the selected message text is highlighted, and then all of the header text. Press Command-C to copy the selection, then switch to your desired destination and press Command-V to paste.