I have Apple Mail version 9.2, but I would like to have the version 10.3. However, I don't want to download the 10.12 mac OS (Sierra) if I don't have too. I currently have mac OS 10.11.3 (El Capitan).
There is a discussion here involving a much older OS (tiger) in 2010:
https://discussions.apple.com/thread/2502383?tstart=0
I can't find many other resources discussing upgrading mail.
Best Answer
Sorry but my guess would be that this is very unlikely if not impossible.
Mail isn't a single self-contained piece of code like a third-party application. Big chunks of the functionality that make up Mail as stored in frameworks that reside in places like
/System/Library/Frameworksfor example Message.framework.So as well as the binary that sits in the
/Applicationsfolder you'd also need to upgrade any relevant frameworks from the/System/Library/Frameworksfolder, and you wouldn't be able to just swap them out because that would break other functionality in the operating system that expected the native El Capitan versions.There is likely a way to do it, but it's such a ridiculously complex task I wouldn't recommend pursuing it.
Sorry.