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Read more:- Convert Outlook Emails to MBOX

Import MBOX files to Outlook [Drag and Drop Method]
Firstly, Install and Run Outlook in System to accessing the MBOX file.
Then, choose the email folder in thunderbird to save them in the EML file.
In Outlook, create a new folder to importing these chosen emails.
Drag and drop the locally stored EML files into Outlook.
Import MBOX to Outlook Using Email Clients
This manual method takes four essential phases to complete the MBOX import process into Outlook 2019, 2016, 2013, and below versions.
Exporting Emails data in MBOX through Thunderbird.
Import MBOX files from Thunderbird to Eudora.
Move .mbx files from Eudora to Outlook Express.
Importing files from Outlook Express to Outlook.
To know the complete process read this guide: – Convert MBOX to PST
Configure Gmail IMAP to Import large MBOX files into Outlook
Login into the GMAIL account.
Click on the gear icon and under Gmail page, open Gmail setting, and choose “Forwarding and POP/IMAP option”.
Choose to enable the IMAP option.
Configure IMAP account and select save changes option.
Note:-To apply the steps of manual methods one must install the thunderbird and Outlook in their local computer or laptop.
Now, run the thunderbird on your local computer.