I don't know what might be out there now that is new...
But I've used EudoraPro for years.
It has always had a ton of features and was ahead of its time.. it can be setup to be very virus resistant too.
The filters could be better but with a little work I get rid of 90% of my spam.
you can set up a ton of different POP accounts and give them all their own sigs and setup "stationery" with stock replies for automatic or manual use on any of them. Wonderful when you handle email for many domains and different divisions of your business.
It is also easy to sort and archive mail and everything can be color coded for quick recognition.
It has a great "find" feature with lots of variables that you use to search on.
It is also Free!.... in a sponsored version that only has one small ad that changes in the corner.
If anyone knows of a better program I'd like to know about it.