I am in contact with the my doctor by email. We exchange about 3 messages per week, today we exchanged 2 messages. Now I have a situation where I think it is a bit silly to write each time Dear Dr. Lastname. For example:
I send him question
Dear Dr. Lastname,
he reply me within 2 hours. Should I write again Dear Dr. Lastime? And the same each time? Or maybe just Hi or just short answer for example
Yes, I confirm.