To access an FTP via macOS X's Finder application, first you will need to make sure File Sharing is enabled.

Go to the Apple menu > System Preferences > Sharing
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Checkmark the option for File Sharing 
Screen Shot 2021-05-04 at 11.17.52 AM.pngOnce that is enabled, open Finder, and click on the Go menu option, and find Connect to Server. Or, you can press ⌘ + K on your keyboard to bring up the Connect to Server prompt.
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On this Connect to Server prompt is where you will enter the FTP URL provided to you via email.

Please Note: If you are looking to retrieve 
Congressional MARC files, please contact us.
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Once entered, press Connect and Finder will open the folder, displaying your MARC files.
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Once accessed, you can also navigate to the sidebar of the Finder, under Locations and access the FTP folder there.

If you have any further questions, please contact us.