dose anyone know if the cast of downton abbey have a Fan mail address?

Well, here are some:

Dan Stevens (Matthew Crawley):

Dan Stevens
Julian Belfrage Associates
Adam House
14 New Burlington Street
London W1S 3BQ
UK

Hugh Bonneville (Robert Crawley):

Hugh Bonneville
Gordon and French
12-13 Poland Street
London W1F 8QB
UK

Maggie Smith (Violet Crawley):

Maggie Smith
Independent Talent Group Ltd.
oxford House
76 oxford Street
London W1D 1BS
UK

Michelle Dockery (Mary Crawley):

Michelle Dockery
Hamilton Hodell
5th Floor
66-68 Margaret Street
London W1W 8SR
UK

if there is any particular actors Fan mail address Du are looking for please tell me and I will try to find it :) I really hope this helped! :D