Somehow I'm pretty sure that Firefox will change the URL www.xn--andr-epa.eu, and I'm pretty sure that Firefox actually should change the URL www.andré.eu...
That doesn't make sense. If you tell it to go to
www.xn--andr-epa.eu that is where it should try to go. If that page redirects to
www.andré.eu it should follow (if allowed). Firefox isn't changing anything.
A patch to use ^\ instead of // is not tested by me, for one because I don't have a PMMail/2 profile which would eventually call the CMD file or EXE. But also because of the described alternatives. Any of Doug's suggestions is reasonable, and far easier than dirty hacks to repair outdated software.
You cannot use \ in place of //. You must use / because this is a URL, which uses forward slashes.
This very thread clearly shows that too many irrelevant initial changes (like a new owner, and a new requirement, and not enough respect for existing paying "customers") is an excellent way to recude the number of active users significantly. I'm not the only one. Banking (or funding) explains an irrelevant problem, but it doesn't justify anything.
Next time one change at a time is a better idea, unless a change is relevant for a paying customer.
You don't seem to know the history. PMMail was purchased from the original authors by BluePrint Software Works (BSW), at one of the v 2.x versions. They did some work on it, to produce the 2.20.2382 version, which was released to previous users (part of the purchase contract). There was also a windows version, at that level. At that time, BSW decided that they would no longer develop the OS/2 version, because the code was a terrible mess. After that, I think they released another windows version, and decided to drop that too. At about that time, VOICE was looking for a bonus for their members, and negotiated a deal with BSW to purchase the OS/2 version (and ONLY the OS/2 version, with a contract that said that BSW retained all ownership to any other version). Then, they could not find the 2.20.2382 version source, and supplied the 2.10 version source (it's a long story). Anyway, James Moe took on the project to get it updated. After many versions where it was mostly code cleanup, PMMail is now much more capable than it ever was before. Some of the problems that were fixed made us wonder how older versions ever worked, at all (and a few things never did work, until he fixed them). Anyway, PMMail v3.x was made available to existing members of VOICE, with an option for new members to pay a nominal fee for it, and all proceeds go toward supporting various OS/2 projects. That is still the case, but the purchase method has changed a little (to reduce the bank charges, which increased the money available to support other OS/2 projects). VOICE, by contract, is not allowed to release the source (although you can get it, if you agree to keep it private, and do some development work). Unfortunately, the only programmer who has really done any work on it, is James Moe, and he has not been able to do much with it in the last couple of years (he does need to make a living, and all development is strictly voluntary), so the project is mostly stalled (but not dead).
So, PMMail 3.x is really a new program, with an old name (there was some debate about calling it VOICEMAIL, but they paid for the name, so they used it). Expecting VOICE to give it away is unreasonable. If you want PMMail 2.x updates, you need to talk to the owner, BluePrint Software Works, which actually doesn't exist any more, and they couldn't release a new OS/2 version anyway (by contract).