There are many other third-party tools available in the web market but only a few of them are reliable. I want to suggest you to use the MacSonik Thunderbird Backup Tool for Mac. This tool helps to save Thunderbird emails to PDF, PST, EML, EMLX, DOCM, DOCX, PNG, JPG, MSG, HTML, MHTML, GIF, etc. It can backup Mozilla Thunderbird emails to 20+ formats and its prominent feature of Eliminate Duplicate Email is outstanding. Using this feature you can remove the same or identical emails from the backup process of Thunderbird emails.
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