Since it's an email address, there's an @ symbol in it. If you enter find mode and pull down the operators drop down from the the tool bar, you'll find that the @ is a find operator and this can produce unexpected results.
To get the @ symbol to not be interpreted as a find operator, enclose your search criteria in quotes such as:
Also, make sure that your email address is of type Text and not number.
Thanks very much. That was all I needed!