CSV ("comma separated values") is a common file format used for text files that contain tabular data. In CSV files, each field of text is separated by a comma, semi-colon, or other special character.
If your email program can export your contact list as a CSV file, you likely can import it into QuickBooks. However, for programs other than Outlook, some fields might not map properly to fields in QuickBooks, and could require a manual cleanup before you finalize the import.