The BNC World shows that that "mail"
is not used a singular count noun (not "a mail").
But it is alright as in "a mail order", "a mail catalogue" etc.
Mails in plural is commonly used.
There are only 3 instances of "email" (an email message,
an email list server, anemal facility), because at the time
when the BNC was completed in the early 1990s,
email was not so widely used as today.
There should be a lot of occurrences of "email" in the ANC.
[本贴已被 xujiajin 于 2005年08月05日 13时54分55秒 编辑过]