How can I add a fixed string to an imask field?

Question

In the documentation we have the following example:

var phoneMask = IMask(
  document.getElementById('phone-mask'), {
    mask: '+{7}(000)000-00-00'
});

I know I can fix characters using {}, but I'm struggling to do this:

XXXXXXXXXXXXXXXXXX@test.com.br

Adding the custom characters in the 'x' places. Is it possible?