Normally EagleFiler will prevent you from importing a file if a file with the same contents (in the data fork) is already in the library. You can check this option if you prefer to import every file, even duplicates. In order for duplicate detection to work, your files’ checksums must be up-to-date. For more information, please read about the Verify and Update Checksum commands.
When you import via Scan for New Files, EagleFiler does not check for duplicates. This is because you have specifically put the files in EagleFiler’s library folder.
To remove duplicates after the files are already in the library, see the Remove Duplicate Files script.
Archived Web pages with the same source URL will generally contain different data, so EagleFiler will not treat them as duplicates. However, there is a script for removing duplicates by URL if that’s what you want to do.
Note: EagleFiler checks for duplicates at the file level. Thus, when you import a mailbox file containing a bunch of e-mail messages, EagleFiler checks for a duplicate mailbox but does not check the individual messages within that mailbox file for duplicates. If you drag messages from a mailbox to a folder, EagleFiler extracts them as individual .eml files, and these can be checked for duplicates.