These labels are no longer used in current versions of Outlook.
One of these labels appears in the address if you select the name from the Contacts list in the Address Book. See the MSKB article Removing the "(E-mail)" from E-mail Display Names for details on how to avoid the label by starting from the Contacts folder itself.
These labels are hard coded in one of the Outlook .dlls.
Since the Outlook Address Book and Check Names display the e-mail type (SMTP, FAX, etc.), you don't really need these labels in many situations. The one exception is with the AutoName feature. For example, if you have two e-mail addresses for Joe and see a red squiggle under "Joe" when you type it in the To box, you can right-click on "Joe" to see the available e-mail addresses. With the patched Contab32.dll, you will not see anything to distinguish the first e-mail address for Joe from the second one. Without the patched .dll, you would see Joe (E-mail) and Joe (E-mail 2).