Various research indicates that we don't multitask well. Anywhere from 5 seconds to 2 minutes is lost when something simple as a buzz, ding or visual interruptions comes up on your device.
Here's a good short into to turning off notification in Outlook: https://support.office.com/en-us/article/Turn-on-or-off-new-message-alert-pop-up-window-9940c70e-b306-442e-a856-d94b20318481
https://scholar.google.com/scholar?hl=en&q=multitasking&btnG=&as_sdt=1%2C44&as_sdtp=