[AtlantaMike]

As of this morning, my phone no longer plays the sound I specified for new e-mail messages. Instead, it plays the default notification sound.
I've tried rebooting, I've tried going to sounds and turning the Outlook Mail sound off and on again, I've tried playing around with all the settings I could find. Nothing else seems to be wrong and I made no changes yesterday that would have prompted this sudden change. I'd love to know if anyone else has fixed the problem, but I'd settle for knowing I'm not alone!

[jmwhite19]

Outlook Mail was recently updated and allows you have separate sound notifications for different configured inboxes like in WP 8.1.

First go to Outlook Mail then Settings > Notifications you can customise the app notification behaviour here

THEN

Go to Settings > System > Notifications & actions

You'll now see your configured inboxes as notification items, you can customise the sounds from there.

I experienced the same issue you have described, and found I needed to change the sound on the specific inbox item and not "Outlook Mail". Because I'm using multiple accounts, the Outlook Mail item no controlled the notification sound, however prior to the update everything was under the "Outlook Mail" item.

Personally I welcome this change as I have my personal and work email and couldn't have different sounds until now!