# Frequently Asked Questions

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## How come this query matches mails in folder:2013? `notmuch search --output=files folder:inbox`

You have duplicates of a message (or messages) in both folders.

Notmuch searches are message based. Multiple files may be associated
with the same message (i.e. the files have identical Message-ID). A
`folder:` search will match the folder of any of the files. The
`--output=files` option outputs all the files of all matching messages.