Yes, it will be recreated if deleted and will be a smaller size. This file is used to index the message folders.

Thank you for your response. Are you absolutely sure this will not damage my email software (because that would be very bad)?

I came across this file because my file backup software had an error trying to copy the file due to a time out (maybe because of its large size) (but I was able to copy it manually).

Are there other such large Thunderbird files that could be deleted and automatically recreated? Is there a list or would I have to find them and ask?

If in doubt, just copy elsewhere prior to deleting. Other files that repopulate include all IMAP mail folders and the smart mailboxes folder that is used to establish unified folders. There may be others,