I am preparing a backup of an IMAP mailbox and have noticed that some messages appear more than once. This may have happened after importing old emails or moving messages between folders. I want to avoid creating an archive filled with repeated messages, but I also do not want to remove emails that only look similar. What should I check before backing up the mailbox?

First, determine whether the repeated messages are actually identical or simply have similar subjects. Two emails can share a subject while having different recipients, dates, or content. The comparison criteria used by the backup software therefore matter. Check whether it compares fields such as sender, recipient, subject, and message body.

It is also useful to review the mailbox folders before starting. Similar messages may exist in different folders for legitimate reasons, so selecting the correct folders and reviewing the results can help prevent unwanted exclusions.

The SysInfo IMAP Backup Tool  documents a duplicate-removal option that can identify repeated emails using supported message fields, including Subject, From, To, and Body. It also offers folder selection, date filtering, and several export formats

Before running a full backup, test the duplicate-removal setting on a small selection of emails. Compare the resulting message count and inspect some of the messages that were identified as duplicates. This helps you understand how the selected criteria behave with your mailbox data.

Keep the original mailbox unchanged until you have checked the exported results. If the objective is simply to create a clean archive, avoid deleting source messages unless that is a separate, intentional requirement.

A duplicate-removal feature can make an archive easier to manage, but the best results come from choosing suitable comparison criteria and verifying the output rather than assuming that every similar-looking message is unnecessary.