I have the same issue, Mail seems to function fine otherwise but I get no sound for arriving mail in "Inbox" or the sound when I click "Get Mail" to force a check - I do get the "Whoosh" on sending though.
Tried booting into Safe Mode and back, no luck - unchecked the sound options in Mail Preferences, deleted custom sound file from Sounds Folder then reversed process, no luck. Do Not Disturb is not set.
This and the fact I lost my Scanner are the only two issues - resolved scanner by deleting/resetting printers, reinstalled both Apples and Printer manufactures software and re Added Printer under Printers & Scanners Pref pane.
Will watch this thread to see if anyone comes up with a fix.