Подскажите пожалуйста какой максимальной длины может быть адрес электронной почты?

alex, по rfc не так, но в отношении адресов почтовых ящегов им (rfc) никто не пользуется+)
всё что там осталось от rfc это "." и "@" +)

QUOTE

rfc0821
--cut
user

The maximum total length of a user name is 64 characters.

domain

The maximum total length of a domain name or number is 64
characters.

path

The maximum total length of a reverse-path or
forward-path is 256 characters (including the punctuation
and element separators).

command line

The maximum total length of a command line including the
command word and the <crlf> is 512 characters.

reply line

The maximum total length of a reply line including the
reply code and the <crlf> is 512 characters.

text line

The maximum total length of a text line including the
<crlf> is 1000 characters (but not counting the leading
dot duplicated for transparency).

recipients buffer

The maximum total number of recipients that must be
buffered is 100 recipients.
--cut

Тоесть 64 + 1 + 64 = 129