Why isn't E-mail capitalized like it used to be in The New York Times?
The 'E' part is an abbreviation, which tend to be capitalised, especially, as others have said, when it's a new term. And abbreviations, through popular use, eventually become a noun in their own right.
However, T-shirt seems to have resisted being lower cased for some decades now, other than the solitary 'tee' which I sometimes see in clothes shops. I wonder whether it's because we like to see the shape of the shirt in the 'T'.
In the UK, about 10 years ago a court order called an 'Anti-Social Behaviour Order' was created - and received many mentions in newspapers. They quickly evolved from ASBO through Asbo to asbo. I think the word was finally integrated when it became, at least in speech, a verb, ie you could have your neighbour 'asboed'.
I can't find anything to verify this, but I think they capitalized it for the same reasons they still capitalize 'Web' and 'Internet' -- they considered it a proper name. Probably even when they did capitalize 'E-mail', they wouldn't have capitalized it in cases like "Sally received an e-mail," but only in cases like "The E-mail servers crashed in Barbados."
Readers had been complaining about E-mail since at least 1995, which gives us the reasoning behind the capital. From the New York Times, August 21, 1995:
P.S. A recurrent gripe, regardless of the vote being cast, involved The New York Times style for writing "E-mail."
"My biggest complaint is the fuddy-duddy spelling 'E-mail,' " wrote Cate Gable of Berkeley, Calif., speaking for many, who wonder why this newspaper uses an uppercase "E" for something that many people and publications write as "e-mail."
The Times style for the term is in keeping with T-shirt, A-frame, H-bomb and other analogous words that predate E-mail. For now, at least, it will stay that way.
In fact, if you read the article from page 1, they're discussing whether An E-mail and E-mails are acceptable terms for a piece and pieces of electronic mail.
Back to the present. The New York Times is still using e-mail and aren't planning to switch to email just yet. But more and more newspaper style guides, including the AP Stylebook, are dropping the hyphen. I expect the Times will follow at some point.