gistfile1.php

<?php

include_once './vendor/autoload.php';

function accountExists($name){
    $soapClient = new \Zimbra\ZCS\SoapClient("host", "port", "username", "password");
    $admin = new \Zimbra\ZCS\Admin\Account($soapClient);
    try {
        // Fetch account by name, if it exists return it
        $accountEntity = $admin->getAccount($name, 'name');
        return $accountEntity;
    } catch(\Zimbra\ZCS\Exception $e){
        // If an exception is thrown check the message, if it matches to NO_SUCH_ACCOUNT message
        // it means there isn't an account with that name thus return false
        // If it's another message something else went wrong, thus throw the exception again
        // so we can catch it later or just log it and die
        if($e->getMessage() == 'account.NO_SUCH_ACCOUNT') {
            return false;
        } else {
            throw $e;
        }
    }
}

var_dump(accountExists('info@foo.com'));