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 "Edit My Notifications" tab and use the "Start/Pause" button.
Click on the "Pause" option if you wish to stop receiving notifications (the "Active" indication will change to "Paused").
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.
For your convenience, the same button is also available under the Account Overview options.
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.