Translation:I sent an email to my mother yesterday.
I am fascinated by this new US English I've seen here: "I sent email". I've never, ever heard that construction before, with it always being "I sent an email" for us here in Ireland, and from my time in England and Wales as well, it is the same there.
"I sent email" seems very clunky to me: although I can see how it has arisen like that, it is unheard of here in Ireland. It reminds me of the American way of counting, "one hundred thirty" for example, with that unanimously being "one hundred and thirty" here and everywhere else. It's fascinating!
I also have rarely heard "you've got mail", with it rather being "you've got some mail". I guess it's all just a difference in dialect!
Even if I only sent one email yesterday, I'd still say "I sent email yesterday" - like "I ate soup yesterday" doesn't say say anything about whether I ate soup once or 5 times, just that it's an action that was performed, whereas "I ate an apple" versus "I ate apples" does have a plural aspect.
Or to come at this from the other direction, how would you say "I sent email to my mother yesterday"? And would you say something different for "I sent emails to my mother yesterday"? :-)
For me, both "I sent email yesterday" and "I sent email to my mother yesterday" are marked forms. They can be used (and only for plural) but are more often not.
I'd just use "I sent an email (to my mother) yesterday" or "I sent (some) emails to my mother yesterday" more often.
Maybe it's a US thing - "mail" doesn't take a plural. Long before email existed, you could send mail, but you could never send mails. "Emails" is used, but usually only to stress the multiplicity of the missive - "I sent you 3 emails already, why haven't you replied?". To use "emails" to refer to the general activity of sending email would be weird.
Note that galaxyrocker is also from the US (as am I).
I see the word “e-mail” in “I sent e-mail” more as a mass noun than either a plural noun or an uncountable noun (such as “soup”). As you’d noted, “e-mails” is used in a way that “mails” isn’t. (“E-letters” would have been a more analogous usage, but that wasn’t adopted, so we’re stuck with “e-mails”.) As such, I see “I sent e-mail” as akin to “I caught fish” — both using the mass meaning — with “I sent an e-mail” and “I caught a fish” being unambiguously singular, and “I sent e-mails” and “I caught fishes” being unambiguously plural. One could say “I caught fish” in the mass sense to mean that only one individual fish was caught (since any group could potentially have exactly one member), but the general meaning would be that multiple fish were landed. I see (and use) “I sent e-mail” in the same light.