None of them is a must anymore when you meet Her Majesty the Queen. In the photo above, former British PM Theresa May curtsies at the beginning of an audience. It is the traditional way: men can greet the Queen with a neck-bow while women do a small curtsy.
Nowadays a usual handshake is formal enough, however, etiquette says you must wait for the Qeen to offer her hand and than shake it politely.
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To address the Queen in a formal way is that you call her “Your Majesty” and then “Ma’am”.
Photo credit: WPA Pool / Getty