How do I decode a base 64 encoded 'attachment' that is embedded in a mail message?

If you receive an e-mail with an attachment embedded within:

1. save the e-mail as a plain text file
2. edit the e-mail and remove any headers

Delete everything before and including the lines that look like:

Content-Disposition: attachment; filename='13234.pdf' ^M
^M

Delete everything including and after the lines that look like:

------------- End Forwarded Message -------------^M
^M
^M

3. At a terminal line, type:

mimencode -u name_of_text_file -o new_file