I disagree with Greg here.
'Below'is a preposition that shouldn't be used as an adjective/identifier like 'back room' or 'top drawer'.
It cannot be used attributively, in other words before a noun to qualify it. You should place it after the noun and an article is also needed: the e-mail [which/that is] below.
However, like many phrases, such use is creeping into English emails (undesirable, IMHO) such as the detested 'I'll check and revert' - Ugh!!
Greg's final solution would be the most ideal version.