In case you have decided not to send any other messages to your customers, either Email or SMS, there is no problem since you can deactivate the Pipeline and cancel all the Queue Items.
Step 1: Deactivate the Pipeline
Although Pipelines cannot be deactivated, you can set an End Date sometime in the past to force it to stop dispatching Queue Items:
NOTE: When you activate the Pipeline back, all the queue items with status Pending will be dispatched as soon as possible.
Step 2: Abort Queue Items
You can abort the Queue Items that are about to be sent using the following steps:
Step 2.1: Filter all Pending Items
On the Distribution Section you can filter all pending items with the filter on the top right corner:
Step 2.2: Select all Items
Then, select all the items and click either "Delete" or "Edit":
On Delete, you will see a simple prompt:
Click "Save" to delete all selected items.
On Edit, the following dialog should appear:
Select "Cancel" as Status and click "Save".
Canceled items can be reset to be sent whenever you like. You can also keep track of the items you had in the Queue.