yet another Apple Mail question

[good-dog at northshore.net]

With a .mac account, is there any settings that make it so you don't 
keep your old messages online?  I'm experimenting with Spamfire and I 
keep getting the same repeated messages being downloaded, plus the new 
ones, obvously.  It says there's 113 old messages online.  The  account 
is not that active.

I'd like to simplify the Spamfire viewing, but am flummoxed.

Thanks.

Mark