If you are still on froyo there's not much you can do about it aside from rebooting at least once a day, or refreshing manually as there is no telling when it will stop working. I had the same problem on froyo. I installed the stock OTA leak of Gingerbreak .588 and report 0 problems with my mail coming in on any client. The GB OTA Stock should be released in the next 2 weeks (guessing) so once you upgrade this should be fixed.
http://forum.androidcentral.com/motorola-droid-x/38201-2-2-progressively-getting-worse.html
thats what i initially found in october when 2.2 came out... none of it was ever fixed even after multiple factory resets... GB it is definitely fixed, the leak has bugs, but the email is not one of them, im guessing the other bugs are worked out