Bug#3901: dotlock" should be setgid mail

["Susan G. Kleinmann" <sgk@sgk.tiac.net>]

A couple of days ago, Lars mentioned
> I suggest staying with rwxrwxrwt.
with respect to the permissions for /var/spool/mail.

Mine is:
drwxrwsr-t   2 mail     mail         1024 Jul 31 13:08 /var/spool/mail/

I couldn't find the debian package that installed this directory, so 
I couldn't figure out if these permissions were "right", whatever that 
means.  So,

a) can someone tell me what package/file/script does install /var/spool/mail?
   (I'd use this info to find out why my search method failed.)

b) Are those permissions "right"?

c) Lars, what did you mean by saying "staying with rwxrwxrwt"?

Regards,
Susan Kleinmann
sgk@tiac.net