Full user review
"Looks, acts like Eudora 7.1 but seems no long live"
Retains old mailbox structure, very flexible message filtering, very easy to configure, multiple servers are no problem. Retains much of the "feel" that made Eudora an email standard for many years.
Not as fast as pre-OSE v7.1 in some key ways, sluggish, a kluge of macros over Thunderbird. Lost the old, easily backed-up *nix-based mail files. Attachments are more trouble to deal with than when they went automatically to a configurable attachments folder. Notifications are much less flexible than with v7.1 (e.g. can't play unique sounds for mail coming in from different people, personal vs business, etc.). Seems to be no longer developed, adding some risk of sudden incompatibility with new protocols etc. if email is crucial to what you do.
The "feel" of Eudora OSE nicely mimics that of the Eudora I grew accustomed to for years, ever since its earliest versions. Eudora OSE also keeps nearly all of the most useful features of pre-OSE version 7.1. Most importantly, it keeps the old, familiar, highly configurable filter functions that send mail to anyplace you want in a directory tree type of mailbox structure. That's all good.
However, OSE lost some of the features I had grown to depend on in Eudora. The one I miss the most is the ability to assign distinctive sound notifications for different correspondents. As a local mail client it also feels sluggish compared to v7.1, probably because it is kluge of macros tweaked to the gills to layer Eudora's efficient email-handling strategy over Thunderbird's very different client approach. Also, OSE hasn't been updated since 2010, so I suspect it is no longer actually being developed. It works okay in Windows 7 but only claims compatibility up to Vista, which does not inspire confidence in its continuing compatibility as protocols evolve.
At this point I'm considering whether to revert to v7.1 (is that even possible, given the completely different mail file structures?) or to reluctantly give it up as a lost cause and move to the labels-not-mailboxes approach of web mail and its local-client mimics (which is how Thunderbird feels to me). A friend uses Firefox for the extensions but Chrome as a fast, unencumbered Gmail client. He says the tactic works great. Or I might try a different client like Postbox. Eudora OSE keeps getting longer in the tooth and may have hit a dead end, I'm sad to say. It feels like the kluge of macros that it is, like at any time it might start to dodder like me. Okay, I'm stuck with me, and I don't want to trade in my wife, but I can move to a different email client. Soon. Maybe.
I don't recommend committing to Eudora OSE at this point. It still does the job for me but only because it's a habit.