Configure OS X Mail
To turn off automatic mail checks, choose Preferences from the Mail menu. At the top of the Preferences window, select the Accounts icon. Then select Manually from the Check Accounts popup menu (if you want automatic checks, set them up in Spamfire).
OS X 10.1
Mail does not provide AppleScript support to start manual checks. The best Spamfire can do is launch the Mail application. Choose "Activate OS X Mail App". Then you can check mail as you usually do.
OS X 10.2 and later