The simplest (but not most efficient) way to do this is to copy the whole profile over to the new machine, then simply delete all the unwanted accounts. A more efficient, but rather more technically challenging method is to set up Thunderbird on the new computer and install the same account. If it downloads any messages, copy these to the Local Folders account. Then close Thunderbird. Open up the Thunderbird profile in the old computer and look for the subfolder under ''Mail ''which corresponds with the account. Open that folder and copy all its contents. On the second computer, find the corresponding folder under ''Mail ''in the new profile, and replace its contents by the material you copied. Then you add in any messages you had previously copied to Local Folders. Note that you should always close Thunderbird before doing any surgery on its profile. https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data