The French have always tried to find their own French-sounding names for every new hi-tech invention; ignoring accepted world-wide norms.
Being French, they are also obliged to decide what gender an object will be; for example, not so long ago it was decided that a computer (ordinateur) should be masculine.
Occasionally they seem to get it a tad wrong. Who, I wonder, amongst the learned members of the Académie française, made the decision that a gentleman's beard should be feminine (la barbe), and a ladies handbag should be masculine (le sac à main).
In the case of Email (electronic mail), the word was already in use; email meaning enamel in French, as in teeth (hence my toothpaste above) or decorated porcelain, so the word was simply shortened to mail.
Mail, as in letters inside envelopes, is designated as being 'male', and is generally called le courrier.