I tried all the suggestions from Diane (and please, I'm not beating on you Diane, in fact, thanks so much for taking the time to post a very detailed explanation of steps to take). I'm one of the lucky ones because I get a sound for "new" email and one for sending email but I'm missing one that's key for me, the "no new mail" sound. The sounds were working perfectly prior to El Capitan and suddenly stopped working after the update (including the change of the new mail alert to the standard one from El Capitan, it didn't even leave the one I had set myself)
- Created a separate user, created a new mail account, same sounds, nothing fixed
- Used the guest account, created a new mail account, same sounds, nothing fixed
- Downloaded the complete El Capitan OS installer, installed it over the previous one, no changes, still the same thing
While appreciate the input for scripts and rules, etc that some people have provided, I'm just shaking my head with disappointment. If I wanted to tinker with quick fixes and bandaid solutions for an operating systems until they got it right, I would own a regular PC and use Windows. I'm tired of trying stuff and since I'm one of the lucky ones that at least gets the "new mail" sound, I will consider myself lucky and just give up. Maybe in a couple of years when Apple comes out with The Admiral or whatever they name the new OS, they will have fixed this issue.
I understand files get corrupted, I understand operating systems have bugs and they get fixed with subsequent upgrades, I understand that nothing is perfect. However, I also believe that Apple has made a name using the trust of its users, a trust in a superior product for which a premium price is paid. That name was backed up by their responsiveness to the users' input when there was something wrong. In this case, neither the product itself nor the response from Apple has been even close to "superior." In fact, I would call it lacking, disappointing, and pathetic. Lesson learned...