[mjevans]

After a given point usenet was nearly 8-bit clean, and thus https://en.wikipedia.org/wiki/YEnc was also developed to convolve all the octets (I + 42 (decimal)) and escape the results that happened to still match reserved characters (CR, LF, 0x0, = (yEnc escape)) - it seems that if the result character was among that set, then = was output and new output determined by O = (I+64) % 256 instead.

[wkat4242]

Yenc is still used a lot actually, for the purpose of what Usenet has de facto become, a piracy network :)

[u801e]

It's too bad yenc didn't take the place of base64 for email.

[jcranmer]

yEnc was rejected by the MIME standardization group for two main reasons, one good and one bad. The good reason was that it has some encoding pathologies, although these could have been fixed in the standardization process. The bad reason was "it's too hard to add a new Content-Transfer-Encoding because you have to change all the user agents", which given that by that time all the clients were changing to support yEnc it was quite clear that uptake would likely of a new addition would have been fairly rapid.