Lotus Notes is IBM email application and stores all emails into .nsf file format # for emails it creates mails.nsf files # and for contacts creates names.nsf files both can be transfered in thunderbird for contacts you can export you address book from lotus notes to csv that can easily import in thunderbid and for mails convert nsf to mbox and import mbox file with thunderbird export import addon for converting nsf to mbox there are multiple utilities available, here is the list of few utilities, please check and migrate your database from lotus notes to thuderbird (free and secure email application) # http://www.nsf.pstfile.org/ # https://www.mailvare.com/free-nsf-to-pst-converter/ # https://www.spikevare.com/lotus-notes/thunderbird/ # http://www.nsf.topstconverter.com/ try these above tools and easy transfer data from IBM lotus notes to mozilla thundebird