Is checking e-mail via Tor Browser secure?

Is it better to use Tor Browser above Mozilla to enter e-mail box, if you do not want to use VPN and if you want to avoid your e-mail provider knows your IP address?

Is this safe to check e-mail via TorBrowser (new session for every check)?

Does Thunderbird program knows your IP?

Yes (if website uses HTTPS)

Anything connects to the internet do so Yes!

It depend on website terms i mean for paypal as example they will block you after time if you kept login from different places everytime, same as google if you logged in from different location you will get that little annoying pop up saying confirm your email or we sent message to you so it depend on website itself

It is overkill
I think thunderbird or a separate firefox for checking email is sufficient.

Any program that connects to the internet, is going to receive/send your Internet Protocol Address, and traffic is going to be sent through the ports a program needs. Tor or a VPN makes it harder to intercept traffic. Gmail has in the past; mistaken traffic through Tor as potentially malicious. So yes, it is fine to use email with the Tor Browser. Just make sure to adjust your security settings in case that you can’t use the website, because some important JavaScript code can’t run; under NoScript.