Greetings should not be used to sign anything off as it is a way of saying 'hello'.
Letters (British English)
formal
Yours sincerely - when you know the name of the person so have addressed it to Mr/Mrs/Ms X
Yours faithfully - when you don't know the name of the person so have addressed it to Dear Sir/Madam
informal
Kind regards
Best wishes
e-mails
These are normally less formal so the informal sign-off as above are usually most appropriate.