I got an email from a new first year student enrolled in my writing class, just a short email, friendly, introductory.
"Hello" was the header it used. Unsure about how to address a professor, I bet.
I sent back a friendly email welcoming the student to NWU and making a short, happy comment about one of the details the student gave.
This was a first for me, though. I don't think I've ever gotten an introductory email from a student before. I've gotten polite inquiries about class stuff, but not a friendly introduction.