format mbox vers pst :
https://www.nucleustechnologies.com/blog/free-methods-to-convert-mbox-to-pst-file/
https://www.outlookfreeware.com/en/products/all/OutlookConvertMBOX2PST

imap vers imap : https://github.com/imapsync/imapsync

How to Configure Thunderbird for Office 365 Using IMAP : https://uit.stanford.edu/service/office365/configure/thunderbird
Configuration de la messagerie Office365 sur Thunderbird : http://media.cneap.fr/42552.pdf
Office 365 (Thunderbird) - Configure Thunderbird : https://kb.wisc.edu/office365/page.php?id=28427#
Office 365 - Which clients/protocols will be supported? https://kb.wisc.edu/office365/page.php?id=28747
How can I get Thunderbird to work with Office 365 ? https://support.mozilla.org/en-US/questions/1176527

Comment configurer Outlook.com ou Hotmail dans Thunderbird ? https://www.numetopia.fr/configurer-hotmail-dans-thunderbird/
Configurer son compte Exchange sur Thunderbird pour Windows : https://docs.ovh.com/fr/microsoft-collaborative-solutions/exchange-configuration-de-thunderbird/
Microsoft POP3 et IMAP4 et configuration : https://docs.microsoft.com/fr-fr/exchange/clients-and-mobile-in-exchange-online/pop3-and-imap4/pop3-and-imap4
https://blogs.technet.microsoft.com/matabra/2013/05/09/how-to-connect-office-365-post-upgrade-to-a-pop-or-imap-account/

Configure the settings as follows:
Incoming (POP3) : Server Hostname: Outlook.office365.com. Port 995. SSL: SSL/TLS Authentication: Normal Password
Incoming (IMAP): Server Hostname: Outlook.office365.com. Port 993. SSL: SSL/TLS Authentication: Normal Password
Outgoing (SMTP): Server Hostname: SMTP.office365.com. Port:587 SSL: STARTTLS Authentication:Normal Password
Username: Your Full Office 365 Login Name"