I am aware that a login to google or whatever other site will leave me unmasked and destroys my anonymity. Yet I still would 'login' from the exit-nodes location, correct? Can I trust Tor, when sending credentials? (e.g. may the exit-node be able to read the credentials or redirect me to another destination?)
The web service will only see the exit node IP. The exit node can sniff your credentials if you send them over a non-https connection.
So by using https you stay relatively secure, it does not automatically mean that you get unmasked, but they can (if they check) see that you connected to your email through a tor exit node, but not what your initial location \ ip is (your home IP etc).