Same problem for me on 2 macs running OSX 10.11.1 beta, I have checked all mail and system preferences, but still no joy. Filed bug report with AppleNo incoming Mail sound since update to OSX 10.11? Other mail sounds OK.
When you say re-establish sounds, what do you mean?It works for me, however, I did have to re-establish sounds after the update. Now incoming mail sound works fine.
Had already tried that, didn't work for meMail, Preferences, New Message Sounds
Had already tried that, didn't work for me
Still broke here. But only works on Imap accounts as well.it seems to work on IMAP accounts and as "hallux" posted it comes in before the mail notification. But does not work on POP3 accounts on my 2015 Macbook Pro 13". I'm running 10.11 public release.
Appears to still be broke in 10.11.2