sub checkmail {
	my $mail = shift;
	return '' if !defined $mail || ($mail =~ tr/\@//) != 1;
	my ($user,$serv);
	if ($mail =~ m/^(.+)@(.+)$/s) { $user = lc $1; $serv = lc $2; }
	else { return '' }
	$serv =~ s/\Q$1// while $serv =~ /([\n\r \])>}'";,])$/;
	return '' if
		!($serv =~ /^.+\..+$/)
			||
		$serv =~ /[^a-z0-9.-]/
			||	
		$serv =~ /\.\./g
			||
		$serv =~ /\.$/
			||
		(($user =~ tr/"//)/2) =~ /\./
	;
	$user =~ s/""//g;
	$user =~ s/\Q$1// while $user =~ /^([\n\r \[{(<';,])/;
	return '' if $user =~ /[^a-z0-9._+&="-]/;
	return $user . '@' . $serv;
}