My T and I are on a first name basis. If she send me an email, she doesn't even closes with her whole name, just her first name.

With pdoc, I actually haven't use his name yet. But he ended his email to me with his first and last name, but not with his title.

With most T's I had to use first names. Even as a teenager. One T actually said that I should use her first name, because that would create less distance (something like that). In Dutch we have two different forms for ''you''. One you use with strangers or older people and then one ''less polite'' that you use with people you know/friends. And with T's I also usually used that one, I was also told by T's I could use that. Though with the more older T's I usually used the polite ''you''.

I think that when you use last names or mr and such, you kind of create some distance.