Hi To entirely delete all account information and old data you need to delete the Profile folder - or tell Thunderbird to ignore the old profile and start a new one. Please note - you might want to keep some things, like maybe your address book, so think carefully before completely deleting the profile. This page explains about profiles, how to find yours, and back it up or delete it. https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data Thunderbird can work with more than one email account, so another option is to add the new email as your primary email account, and still keep the old data. Hope this helps, Agnes