[blacklion]

My bad, I've dug dipper into the problem now and now see, that this is really a problem.

You are right.

But, again, what is simpler: add feature to existing OSS project or write all new protocols?

Second is more fun, for sure, I can understand that as programmer myself.

[Avamander]

This extension amongst other features has not been implemented in Dovecot for a long time now. If it were easy (or easier) I'm sure it would be there already.

I do get the sentiment that building on top of old is usually better and more efficient, but this unfortunately does not carry over well to the entire ecosystem and each project. So it's better to replace in some cases, maybe not with a new protocol but a new implementation.

But to answer your question, you can actually do both. Stalwart both added the feature and support for all new protocols. It didn't take a decade either.