I haven't tested this one, but here's an easier (if much less permanent) method to accomplish the same thing. A quick check of Mail's preferences file reveals that the refresh value is held in the RSSPollTime key. You can easily change it in Terminal (quit Mail first) with this command: defaults write com.apple.mail RSSPollTime nn, where nn is the desired refresh interval in minutes. The downside of this method is that if you ever even open the RSS panel in Mail's preferences, your setting will revert to whatever shows in the pop-up menu in that panel. The solution in this hint is permanent (at least until Apple updates Mail), and provides a menu item to let you easily see and select the new value within Mail
Does not appear to work for me :/ – Antony Stubbs – 2011-12-29T19:51:23.130
@Koning anytime bud – admintech – 2009-10-29T13:18:50.767