There are two parts to consider in this question, with the first being the Outlook mail client local to your computer (which you can connect and use through many webmail services) and the second being the configuration of the email server or webmail service behind the Outlook client (such as Exchange, Microsoft365, or Outlook.com). Which part is the most important to you is dependent on your current email provider and method of syncing email, with either the POP3 or IMAP protocols. POP3 is generally for local storage and management of email and folder structures and deletes the email from the server on disconnect and is much less common today. IMAP is generally for management of email and folder structures on the mail server or webmail service. Here is a place to learn more about the differences: https://support.mozilla.org/en-US/kb/difference-between-imap-and-pop3.
To address the first situation, POP3, it is unlikely that this situation is how you’ve been operating in recent years, with all mail stored locally on your device and not on the email server. If this is the case for you, however, transferring email and settings from your local Outlook client to your new Thunderbird client is technically very challenging and potentially privacy-invasive, requiring a number of steps, and not something we recommend.
This leaves the IMAP approach, which is much more common. This depends on the email server or webmail service and its configuration, but generally, email and folder structures are transferred into Thunderbird. It is usually not a perfect one-for-one transition, but will get you most of the way there. Not all email servers or server configurations may support folder structures in exactly the same way as Thunderbird. Here is a link to Mozilla’s instructions for automatically connecting Thunderbird with an IMAP email account: https://support.mozilla.org/en-US/kb/automatic-account-configuration.
Also, if you’re using an online, webmail version of Outlook or similar Microsoft email account and have multifactor authentication (MFA) configured, which we always highly recommend, then you will need to generate a Microsoft App Password for your Thunderbird client. Here is Microsoft’s instructions for doing so: https://support.microsoft.com/en-us/account-billing/using-app-passwords-with-apps-that-don-t-support-two-step-verification-5896ed9b-4263-e681-128a-a6f2979a7944.
And if you’re using ProtonMail, which is our preferred, privacy-friendly email provider, you’ll need to use the ProtonMail Bridge application to use Thunderbird as an email client to pull email from ProtonMail. There are instructions using the ProtonMail Bridge app are located here: https://protonmail.com/support/knowledge-base/protonmail-bridge-clients-windows-thunderbird/.