If you want to save the text of multiple messages in Mail, you can select them and then go to File > Save As. The familiar dialog box will appear, where you can specify a name and location. By default, the messages will be saved in Rich Text Format; you can also opt to save them as plain text or as Raw Message Source.
The only problem with this is that it saves all of the messages’ contents, including the headers. If you’d rather save just the text, a tipster on hints.macworld.com came up with an AppleScript to do the job.
To implement this fix, open AppleScript Editor; go to www.macworld.com/6809 and copy and paste the script from there.) However you acquire it, the script needs to be saved to /Library/Scripts/Applications/Mail Scripts and given a name (Save Text of Selected Messages, for example).
To use the script, first make sure the AppleScript icon is showing in your menu bar; if it isn’t, open the General tab in AppleScript Editor’s preferences and enable the Show Script Menu In Menu Bar option.
Next, open Mail and select the messages you want to save. Then open the AppleScript menu from the menu bar and select your new script from the Mail Scripts submenu. TextEdit should then open a new document containing the text of the selected messages – just the text of those messages, without the headers.