Why Muslimah can't shake hands with man?

A British man came to Sheikh and asked:

"Why is not permissible in Islam for women to shake hands with a man?"

The Sheikh said:

"Can you shake hands with Queen Elizabeth?"

British man said:

"Of course not, there are only certain people who can shake hands with Queen Elizabeth."

Sheikh replied:

"Our women are queens and queens do not shake hands with strange men."

source