I was trying to add my grandparent's e-mail to my Gmail contact list, but gmail kept telling me "Please make sure the email address you entered is valid." I figured it probably wouldn't import it because they were using something of a non-standard address.
The culprit here happens to be the ampersand sign. I realized that gmail also has a contacts import option which allows you to import contacts from a CSV file. A CSV file is essentially just a text file with values separated by commas. It essentially allows you to put tabular data into a non-proprietary format.
Editors Note: There is not supposed to be a space after the ampersand, but for some reason my blog software keeps adding it.