MailsDaddy MBOX to pst Converter Tool is the most accurate program to load heavy mailboxes and export them to pst file format without any hassle. It can be used on any mbox-based email client to convert Emails files to pst. If you want to move selected mailboxes to Outlook, then this solution also works for you.

Read more: MBOX to PST Converter

Read the Manual method here: MBOX to Outlook

For Mozilla Thunderbird: Convert Thunderbird to Outlook