Unfortunately Eudora is basically three completely different codebases (Windows, Mac, and a rebranded Thunderbird for Linux). I guess only the Windows one is likely to ever be revived.
So it's the CHM who is barring people from using the name. The relevant clause must be this: "Neither the name of Computer History Museum nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission." Is this really "BSD license", if the name is off-limits? This looks like an extra clause to me. Honest question.
EDIT: also, that clause mentions the names of contributors, not of the actual software. So they would have to argue that Eudora is barred by "contributor Eudora Inc." -- does that company even exist anymore?
You can have Firefox branding if you compile it yourself, but you can't distribute the binaries (Gentoo has a notice about this in the build process). This is why Debian created the IceWeasel package.
The museum might want to preserve the name associated with that piece of history, so Eudora always points to that final release. If the license for the code is BSD, people can of course publish their own ports with new names.
There's actually a few licenses that are called the BSD license. In modern terms, BSD refers to the 3-clause BSD.
However, the 3-clause BSD was not the original form. It was introduced because the 4th clause was generally viewed as problematic. That 4th clause is:
> 4. Neither the name of the <organization> nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.
This "weird" clause is actually the 4th clause of the 4-clause BSD. It's weird because it's extremely uncommon, but it is part of a major BSD license.
3. All advertising materials mentioning features or use of this software must display the following acknowledgement: This product includes software developed by the <organization>.
> The Windows version of Eudora is written in C++. The source tree consists of 8,651 files in 565 folders, taking up 458 MB. There are both production (“Eudora71”) and test (“Sandbox”) versions of the code.
> The Macintosh version of Eudora is an entirely different code base and is written in C. The source tree consists of 1,433 files in 47 folders, taking up 69.9 MB.
[0]: http://www.computerhistory.org/_static/atchm/the-eudora-emai...