Q: How to fix the mail sent (whoosh) sound when disappearing intermittently

In the Notifications pane of System Preferences, uncheck the Do Not Disturb boxes.

After a long consultation with Apple, nothing worked to fix the absent "swoosh" in outgoing mail but turning off the "Do not disturb" in Notifications did the trick. Thank you so much. Like Pavlov's dog, I could not live without hearing the "swoosh". Life is good again in email land.

Hey Linc - thanks so much for always being on top of questions in these forums! Your help is priceless...

Thank you Linc!!!

I tried a bunch of the suggestions but what worked (and I found odd) was that even though I had turned off "do not disturb" in system preferences> notifications> do not disturb, when I went to the actual notification center in the upper right corner of my screen, "do not disturb" was still active.  I turned it off there, and now I have sounds again.  If you don't see it right away, scroll upwards because it sometimes hides above what you see, not sure why they make it do that.  I find it odd that turning it off in one place doesn't affect the other.  Here's a screenshot of where to look....

Wow. You're good.  Apple should hire you.  Fixed my swoosh problem.