Well, yes. It's a valid email structure... Which is passing validation. Whether it's a valid, existing email address is a different matter. In which case, I'd suggest no it's not.

This kind of validation goes beyond general email validation and falls under 'does the email actually exist' validation. Which is a different matter.

Yes, I've solved it using try {}

    try
    {
        $this->mc->lists->subscribe($list_id, ['email' => $email]);
    }
    catch (\Mailchimp_Error $e)
    {

        if ($e->getCode() == '214') return '214';
        elseif ($e->getCode() == '-100') return '-100';
        else throw $e;
    }

code above is in event, I just don't like that I have to take care of "validation" like this; known errors from mailchimp are send back to controller...