Using your email on Tor is a bad idea because you potentially lose your anonymity, login on anything could affect your anonymity, specially sites not using HTTPS, just like this forum.
If your email provider uses HTTPS, practically all of them do, your credentials and stuff you type should be encrypted by HTTPS protecting them to be eavesdropped in Tor exit nodes.
What you can do if you want to use your email on Tor is to open a Tor session exclusively to check your email, then restart the session in Tor and do your browsing.