Microsoft product keys normally do not contain vowels. This is done to
prevent the occurence of real words in the product key which could be
considered offensive by someone. So if the 'key' you are holding contains an
"E", it's most likely not a Micrsoft product key.
(Next to vowels, there are other characters/numbers which cannot be used in
a product key to ensure readability.)
Depending on where you bought the software, you could ask them to mail you
your key again. There's no guarantee they keep a copy of it, but it could