Lin here:
I am no longer a super e-mail user, but I have been "on the net" for a long time, and therefor have a huge collection of valuable e-mail all in various formats. I have retired from active searching for the perfect e-mail program. I use what works, and backup daily. Things change and I have accepted that fact. My current system is low cost, flexible enough, and secure in the sense I have not lost an e-mail in 13 years. The main idea is that an ideal net correspondence system must solve two or three problems, and no one program can do it all. Also it must be flexible enough to allow for future innovations.

What I currently use is Apple Mail, as a front end. It does what I need it to do. Read and write quick responses. It allows me to use "Aspell", "GPG", "PGP", and some IMAP functions. In conjunction with "CopyPaste", I can whip through the daily deluge fast and simply. Add to this mix "ZOE" as an archive, and search tool, and a reliable back-up strategy, and I can easily find that one e-mail I wrote 6 years ago, or who did I "bcc" in 1991 about "love". "Zoe" is slow and cumbersome to set up. But the user interface is clean and can not be beat for indexing, and finding that cross reference. No this is not a perfect solution, there is no perfect solution. But it works well, it's cheap, and it allows for the next hot new thing. (perhaps integration of RSS, or XML, or video chat into an e-mail system.)