Dynamically select multiple value in dropdown

I have made multiple select dropdown in form

[select* fieldname multiple include_blank class:q_inpt1 "test1city|[email protected]" "test2city|[email protected]" "test3city|[email protected]" "test4city|[email protected]"]

Now, my question is How to auto select default values when contact form load, I have list of Mail id and known those mail id’s should be load.

For instance when page contact form page load then auto select drop-down value “test2city” and “test4city” behalf of mail id “[email protected]” and “[email protected]”

Sorry for my English.