Hopefully, the data you are talking about in conjunction to your e-mail is in the form of attachment ... a file.

If that is the case, you want to save the file (files) to your computer's hard drive (disc).  Depending on your e-mail system, if you click your mouse on the name of the file you will get a list of choices of what you want to do with the file.  (In some systems, this is a right-button mouse click.  You may also have to indicated that you wish to allow the download (file saving) before you can proceed further.  This process is a function of your virus protection software and/or firewall.)  Select the "Save As" option and your computer will respond with a window indicating where it is about to save the material and its file name.  These default choices (location and name) may be OK with you, but I find it desirable to keep mapping files mostly in the same general locations  (and not necessarily "My Documents").  It is generally NOT a good idea to change the file name extension (the part following the period in the full file name, as this is often used by software as a "recognition symbol".)  In any case, once the file is saved, you can then go to your Garmin Mapsource and open the file.  If it is a compatible file, then it will be loaded (you may notice changes to the content of whatever was previously in the left window of your screen, where current "resources" are listed.  However, you may not see them on the map (unless the last map viewed was for the same general area as the positions indicated by the new data).  The quickest way to get all parts on the "same page" is to click on one of the items in your left-window and then ask the software to show that location on the map.  (One drawback of the software here, in my opinion, is that it will zoom to a level that magnifies that location ... which means you'll need to zoom back out to get a meaningful perspective).

Let me now how this works and then we'll talk about something more complicated.  Also, I'm doing this off the top of my head and I could have omitted something important.

dd