I can only recommend Gnus, because I don’t know any other email clients. I agree that it isn’t for everyone. In this case I recommended it because someone claimed that they couldn’t use email for development because they would end up spending all of their time managing their email. I’m confident that Gnus’ scoring feature would fix that, but at the same time I don’t really believe that the complaint was a genuine one; all email clients have some form of filtering that can do 90% of the work for the user. And most servers support Sieve, which works regardless of what client you use.

BTW, Sieve beats an ad–hoc Python script any day of the week :)