I'm in exactly your situation. MailHub hasn't worked for me in quite a long time due to my OS upgrade. Dervish Software for a while had a website and a forum, but the developer has been absent from both for several years, and now they are both shut down.
So MailHub is gone. I know people have tried to contact the developer via snailmail and even offered to purchase the code. I've never seen any report of updates or new versions, so my assumption is that it's never coming back.
Re Email Filing Assistant. I use it daily because I can at least get my filing done quickly. But its promise of being able to send and file has never worked for me. Its predictive filing ability is spotty. It crashes from time to time. It requires a separate window. Considering that Apple Mail's own predictive filer is decent, EFA serves me more as a backup, but one that is very handy. EFA also has some additional features that I don't make use of and that don't exist at all in Apple Mail. So whether it's 'good' or not depends on your needs.
I've also checked out all the other plugins for Mail I can find, and at this time I've not found anything even close to MailHub. There is a full-featured program called Mail Butler, but it is geared more for enterprises and thus has its developer feasting on your wallet via an expensive subscription plan.
I'm wondering whether it's time to switch mail programs, but I'm not that desperate yet. I'm curious about the open source Thunderbird but have not fully explored it. Unless it has a robust autofiling program there's not much point in my switching.
