I had to move my Riseup account over to Thunderbird because something went wrong when I had NoScript enabled. I'm looking to do the same thing with my Sigaint account, which I almost never use unless a vendor is having problems communicating when I use Riseup. I don't know if they use IMAP or POP3, and the autodetect system failed.
Only if you upgrade. $30 lifetime.
I just got turned on to openmailbox.org it comes into t-bird quite easily, figured out how to use pgp with the two. Just barely made it. Lots of practice. Not a geek.