I have the free non-premium version and found this option, which doesn't say anything about needing to pay a fee. So it looks like if you have some other account in T'bird, you could access your Outlook mail through that. Page sez:

Email forwarding Inbox > Options > Email forwarding

You can forward your mail to one other email account.
Important note: Please sign in at least once every 365 days—otherwise your account looks inactive and could be deleted.

[TICK BOXES & DIALOGUE WINDOW]:

Don't forward

Forward your mail to another email account

Where do you want your messages to be sent?
Example: name@example.com

Keep a copy of forwarded messages in your Outlook inbox.