If you wish to stop receiving Notifications, there are multiple ways to pause or delete those that you have already created.
Simply, select the "Notifications" option under the My Account Section, click on the "PAUSE ALL" button.
This way, you may pause all your notifications for as long as you wish (regardless of the Communication Channel you have selected).
Note that your existing sets of Notifications will not be deleted so that you can easily activate them again at any time by clicking on the same button.
At the right side of each set of Notifications that you may have created, there is the "X" button which you can use to permanently delete the corresponding Notifications and, thus, stop receiving them.
Note that this action has permanent effect. If you wish to re-start getting notifications for the same asset (Vessel, Fleet, Port), you will have to create them from scratch.