Хоть телепаты из отпуска так и не вернулись, попробую угадать: мейл-сервер у тебя под виндой.
В таком случае это для тебя:
The Windows implementation of mail() differs in many ways from the Unix implementation. First, it doesn\'t use a local binary for composing messages but only operates on direct sockets which means a MTA is needed listening on a network socket (which can either on the localhost or a remote machine). Second, the custom headers like From:, Cc:, Bcc: and Date: are not interpreted by the MTA in the first place, but are parsed by PHP. PHP < 4.3 only supported the Cc: header element (and was case-sensitive). PHP >= 4.3 supports all the mentioned header elements and is no longer case-sensitive.
Переводить, надеюсь, не надо?
