Seems to me if we, the OS/2 community, have access to the source code of PMmail and can make whatever changes or fixes that are needed or desired, then that is close enough to open source.
We have the source. The problem is, that we don't have the volunteers to do the job, within the limits of the purchase contract. If VOICE hadn't bought it, PMMail would have been totally obsolete, long ago. At least it is still usable, thanks to volunteer help, but it does need a lot of work to keep it viable.
PmMail is a strange animal that works well in so many ways, and at the same time has some ah, interesting, design issues. Like storing messages as files and using Presentation Manager containers as the user interface.
The messages are stored individually, exactly as they are received from the mail server (with required header additions, such as time, and date received). That actually makes them usable as legal documents (or, it did, at one time). Storing messages, in that way, is not a problem.
The basic design was actually quite good. The implementation that VOICE got, was full of examples of how to do bad programming. Most, if not all, of the worst examples got fixed, but there are still a lot of things that are "not perfect". One of the main problems, is using the PM Container for the user interface. The limit for the number of messages in a folder, seems to be somewhere near 20,000 (depending on a lot of things). The usable limit seems to be about 10,000 in any one folder, and if you want any kind of performance, 1,000 messages, per folder, is pretty much the limit. The indexing scheme is partly responsible for poor performance. It turned out, that the chosen XML engine is designed to be slow. There is another XML engine, that may be faster, if anybody knows how to implement it, but containers need to be replaced by something else too. Using a container for the actual display is good, but it needs to be changed to display a small portion of the message lists (sliding window), with the actual data stored in a different way.
There is also the PMMSEND program, that is a part of PMMail. It has not been kept in step with PMMail, but it still works, with a few work arounds implemented. I am not sure if anybody actually still uses that program, although I should do one monthly mail out using it. I just haven't got around to doing it.
One of the most demanded features, is Remote Control, where the user can list all available messages, and handle them individually, before downloading them. That feature (mostly) works, in spite of the fact that such a thing is not, at all, supported by mail servers. It takes a bit of practice, to learn the tricks, but those who use it, love it. It is mostly needed for high volume mail, on a dial-up network, but I am sure that others use it, just because...
Decent Email programs seem to be in short supply on all platforms, at least to hear people bitching and now a lot of people use web mail in a browser.
Web mail, seems to be a work around for the problem. It also makes it much easier for companies, like Google, to spy on what you are doing, and add advertising to your messages (IMAP is used for the same thing). If you read the fine print, you specifically allow them to do such things, when you use their service. Of course, e-mail is generally not a secure thing anyway, even when you use the so called "security features".
Of course, the "replacement" is in the facebook, twitter, etc. world, which is specifically designed to feed back information, and add advertising. I am not sure why anybody (especially certain politicians

) would even think about using those things.