For a long time, Bryan Garner and LawProse were defenders of the hyphen in e-mail. No longer. We’re realists.
This type of question—e-mail or email—depends on actual usage. From the inception of email in the late 1970s, the word was predominantly hyphenated. (Same with e-business, e-commerce, etc.) In print sources, the turning point came in 2012: that’s the year in which, in books at least, the solid form overtook the hyphenated form in frequency of use. Today the solid form predominates by a 2:1 ratio in books. The ratio is much higher in other types of writing.
The Chicago Manual of Style acknowledged the shift in its 17th edition of 2017.
If you’ve been a stalwart hyphenator and intend to continue, just know that your communications will strike people as ever more quaint. The hyphenated form didn’t stand a chance against the tech companies’ bombarding people with the solid form—billions of times a day using email. And so:
Email once had a suitable hyphen.
It was sucked out as if by a siphon.
Some persisted in e-mail,
Which, just like a fee tail,
Smells of the old-fashioned gryphon.