Well I found a page with a tip from Johnnygozy:

I think I’ve figured out a solution for this problem. If you click on the mail icon, then hold down command and option keys while clicking on preferences in the drop down box, you will be prompted with a box that has a key and value prompt. Type “AutocheckInterval” under key (this seems to be case-sensitive) and then under value type in the number in minutes of how often you want it checked. You will need to quit out of the notifier (again found in the drop down box under the mail icon) and then run the app again for your change to take effect.  I typed in 1 and it is checking every minute or so now for me. I hope this works for everyone else too.

This worked perfectly for me, but some users are experiencing trouble.  Give it a try.