What's wrong with this expression?

["Daniel Serodio (lists)" <daniel.lists@xxxxxxxxxxxxx>]

I'm trying to troubleshoot a script that works with bash but fails with 
zsh, and it uses the "regex match" operator. What's wrong with this 
expression?

    [[ "foo" ~= "x" ]] && echo true

Fails with "zsh: condition expected: ~="

Thanks in advance,
Daniel Serodio