POP Server mailboxes

[AZ Pete]

Hi all,

I've set up a pop3 server on a machine and all is working ok.  I am able to 
download my mail using an email client from a couple Windows test boxes.
I am, however, receiving the following error in the maillog whenever I 
retrieve mail:

'Mailbox vulnerable - directory /var/spool/mail must have 1777 protection.'

In reading the chmod man page this would give permissions of rwxrwxrwt.
The 't'  means "save program text on swap device."

In one of my Linux books it mentions a capital T, which means the sticky 
bit is set.
A small 't' would result if world sticky bit is set along with world execute.

Does anyone have any clarification as to what the lower case 't' permission 
actually does?
Do I need to apply it to the /var/spool/mail directory as the pop3 error 
message indicates?
Or is it simply one of those 'nag' errors where I can leave it be?

Any help would be appreciated.
Thanks,
Peter