Description of filename in Maildir/cur

[Reid Sutherland]

971829536.26305.simple:2,ST
971856803.14682.simple:2,T
971871879.5249.simple:2,RST

The first part is I'm guessing is unix time(). Second part is the inode?
Third, host. Now what's this 2? And what's T, ST, and RST?

thanks

-reid