what's this .cache file and why it remains

[PM WONG]

Just got 4.0.3 running.
I tried server-mode for specific user. (i used the method of
creating a .user.qpopper-mode file under /var/spool/mail)
But i discovered that there's a file called
.username.qpopper.cache being created under /var/spool/mail
and it remains there forever.
What's this for and could i delete it ?

Thanks
Pui