For secure, and fast migration of Thunderbird to Outlook, you can use an automated tool such as Stellar Converter for MBOX. Since Thunderbird stores the mailbox data in MBOX files, you can use the MBOX Converter tool to convert the MBOX file to Outlook importable PST file. Stellar Converter for MBOX supports 15+ MBOX file extension email extensions such as Thunderbird, Entourage, Spicebird, Pocomail, AppleMail, etc.

Stellar Converter for MBOX offers the following advantages:

• Converts Thunderbird MBOX files to PST in a few easy steps
• See the preview of your emails before performing the final conversion
• Exports Thunderbird emails to Office 365, PDF, HTML, EML, MSG and RTF formats
• This tool offers advanced filters to export only selective Thunderbird emails to Outlook
• You can save converted PST file as a new PST, or you can add on existing PST

For more info you can search on Google Stellar Converter for MBOX.