Although, to be honest, email standards are a complete mess in some regards and I suppose this make such an endeavour not as trivial as it looks on first sight.

Just an example: try to create (and use) an IDN-based email address with non-ASCII characters in the local part. You will be amazed how incompatible on so many layers this actually is. I can hardly imagine there weren't dozens of similarly tricky situations where the developers of this, or any other email client for that matter, were forced to make quite serious design choices because of either ambiguity in standards, or widespread lack of support thereof.