From Bryan Garner’s LawProse Lesson #364:
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.I like the consistency of e-noun, no matter the noun, and have no plans to remove hyphens from my 2005 post How to e-mail a professor. I’m content to have my communications strike people as ever more quaint. Just look at some of the meanings of quaint : “clever, ingenious; wise, knowing; skilled” (OED). Granted, those meanings are obsolete.
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