The article here: http://kb.mozillazine.org/Filters_%28Thunderbird%29 explains that filters are account specific. It also suggests using the global inbox (with filters for Local Accounts) if you want to combine a number of POP accounts: would that do what you want?

Thanks for that reply, but I had already read that article as well as a few others concerning filters.

What I am doing is putting all my filters on the primary account from all the other accounts. I am also using sub account filters to move all messages inside each sub account to the primary account so all the filtering will be done by the primary account for the major sorting.

I close Thunderbird and then begin editing the msgFilterRules.dat file in the main account with a standard text editor by cutting and pasting each sub accounts existing msgFilterRules.dat file information into the primary msgFilterRules.dat.

That you would think would do the trick, however after I save and exit that primary msgFilterRules.dat file, when I start Thunderbird up again, all my changes that I inpoutted into the main msgFilterRules.dat file have been overwritten with the previous msgFilterRules.dat rules somehow, and none of the ones I inputted into the file exist in that main msgFilterRules.dat file any longer.

Any thoughts ????