The export function that creates a zip file also has a reminder not to exceed 2 gig. If that import doesn't work, you might try this:

1. click tools>export and then click the 'open profile link'
2. now exit thunderbird
3. highlight the entire profile and copy to external media
4. on win 11 pc, repeat steps 1 and 2
5. now highlight and delete the contents of the profile and paste the contents copied to external media
6. start thunderbird on win 11

Thanks for getting back to me, problem is on the win7 version, (115.18.0 (32-bit), the only option is to export as a zip file.

I tried copying the profile folder to the win7 pc and importing that but it says nothing to import

Then do this:

1. click help>troubleshootinginformation on win 7
2. scroll to 'profile folder' and click 'open folder'
3. now exit thunderbird
4. highlight the entire profile and copy to external media
5. on win 11 pc, repeat steps 1 and 2
6. now highlight and delete the contents of the profile and paste the contents copied to external media
7. start thunderbird on win 11

Thanks again for the help. On both win7 and win11 there are local and roaming profiles. On the win7 pc they are both called 6kqqg7m3.default

On the win11 pc there are several profiles, one is also called 6kqqg7m3.default I replaced these in both local and roaming from the win7 pc, and although it loads OK Thunderbird is still 'blank' with no accounts or emails. Have I messed up ?

In the end I installed 115.18.0 on the win11 pc, copied the whole Thunderbird folder from apps roaming to the win11 pc and all was fine.

Will be careful with updates !

Many thanks for the help