I received an email notifying that my colleague and I have been awarded a fellowship, sent by an administrator but signed by the director of the programme which is a professor. The institution in based in the US. The professor and another administrator are copied in that email. The only instruction in the email was to contact an administrator notifying them of my acceptance.
What is the appropriate response? Should I reply to the initial email thanking for the fellowship in addition to writing the administrator? Should I include the director of the programme?
Being based in northern Europe, my initial impression is that a "thank you" email sent to everyone's mailbox would be an annoyance, but I'm completely ignorant of etiquette in American academia. Would a lack of a thank you email be seen as a lack of gratitude?