I have never seen a "drag and drop" mechanism to add multiple entries to contacts, though I won't swear that some e-mail client might not have that.
It's far more conventional for the source to export the group contacts to a CSV file and for the recipient to use the import feature of contacts to bring those in.
Brian - Windows 10 Home, 64-Bit, Version 1809, Build 17763
Explanations exist; they have existed for all time; there is always a well-known solution to every human problem — neat, plausible, and wrong.
~ H.L. Mencken, AKA The Sage of Baltimore