I think it my struggle when there are a lot of files, maybe over 2000. But I haven’t verified this

Hi Russell,

Thanks for reaching out to us.

As for Delete All Transactions, this is meant for the historical entries i.e., the processed entries. However, if the file is in Unsent status, the application cannot read the files for them to be deleted. You can work around this by choosing one of the following options:

• Deleting the files from the respective Send directory on disk - The Send folder holds input messages or messages that are queued to be processed by the Connector.
• Copying the Connector - Right-click the Connector and choose Copy Connector feature - This creates a copy of the configured connector with a new Connector ID. While all of the configuration settings remain intact, the transactions will not be inherited.
• Turning the automation off - so the files are not accumulated in the Input tab further if there is any process that's been pushing the files for it to be processed by the given Connector. 
• Right-clicking on a connector and select Show Error Path you can create an alternate path for files that have already failed to send for the maximum number of attempts. If you create a new Script connector without any script configure, this will simply dispose of the messages. If you use the Show Error Path to configure an error path to an unconfigured Script connector, attempting to send the files by choosing 'Select All' - will route the files down the fail path to be disposed of, and the history of those failed files can be deleted using Delete All Transactions. 

I hope this helps, let us know if you need more clarification.