Some of the emails you present are straightforward and useful - the second one in particular I'd be happy to receive. If you feel like someone would be a good fit after improving their skills in some specific area, that's a good thing for the candidate to hear.
Others, though, feel downright insulting - especially the first email. Praising someone's programming background, past projects, and eagerness to solve hard problems isn't an appropriate lead-in to telling them they failed a technical interview. It's either vacuous (they weren't talented, but you needed something to compliment) or back-handed (if their technical skills weren't good, how can you actually respect their past projects?) That's just a way to leave a candidate feeling worse about themselves and you.
Don't abandon this idea. I hugely value specific rejections, even blunt ones like "You don't have the skills we need" or "You failed the second technical interview". Just don't mix that with praising traits you're about to reject someone for.
Others, though, feel downright insulting - especially the first email. Praising someone's programming background, past projects, and eagerness to solve hard problems isn't an appropriate lead-in to telling them they failed a technical interview. It's either vacuous (they weren't talented, but you needed something to compliment) or back-handed (if their technical skills weren't good, how can you actually respect their past projects?) That's just a way to leave a candidate feeling worse about themselves and you.
Don't abandon this idea. I hugely value specific rejections, even blunt ones like "You don't have the skills we need" or "You failed the second technical interview". Just don't mix that with praising traits you're about to reject someone for.