Here is Outspring's recommended strategy for dealing with unwanted messages:

1) Find all the unwanted messages in the "Quarantine Folder". You may find column sorting and "Quick Search" useful for finding unwanted messages. See the section on "Quick Search" for more details.

2) Delete all the unwanted messages using the "Delete" action

Note: You can't undo the delete action.

See the "Message Actions" section for more details on the "Delete" message action.

Deleting unwanted messages prevents Spamphibian Gateway from using up disk space. Additionally, certain actions will be slower when you have lots of messages in the "Quarantine Folder".