I am using Macbook pro 13inch 2015 model. Using OSX Sierra.
Every time I send a mail with the apple mail client is makes a woosh sound. In order to suppress this sound I have done the following things
- Go into settings -> notifications and switch off the notification sounds for mail client.
- Disable User Interface sound effects in settings -> sound.
However still when I send a mail it makes a stupid woooosh sound.