I think the easiest way is to import the Outlook mail to MailStore Home, then export it to eml files that can be imported to TB by simple drag and drop to Local Folders.

https://support.mozilla.org/en-US/questions/1320667

Thanks for your suggestion but, I just succeeded to import all my Outlook 2007 Mails, Archives, Maps and Contacts using the Standard Import option of Thunderbird in two separate actions. Outlook 2007 was installed on the same laptop so I didn't had to generate any export file from Outlook. I wasn't aware of this possibility. Just started yesterday using Thunderbird. The only things I'm still missing are my calender items/appointments. But thanks for your reply anyway. Best Regards,

Rik

I'm glad the Import function worked for you, as this is the first time I've heard of a successful transfer with TB 78. It's usually necessary to use an older version of TB, 17 or 31. There may still be a bug where 'Import everything' fails, although chosing mail and contacts separately works.

To import the calendar, save it in .ics format from Outlook, then import to TB:

https://www.datarecovery.institute/outlook-calendar-to-thunderbird/

I just succeeded to export all my calender items with complete information about all my appointments out of Outlook 2007 as an ICS file and imported this file into Thunderbird 78 without any problem. Now I have all my Outlook 2007 information in my Thunderbird mail environment and can definitely close my Outlook Mail. Thanks to you all

This maybe important : Forgot to mention in my previous reply but I only used standard functionality that's available in Outlook 2007 and Thunderbird 78