Parameters 发送带有mailgun无效参数的消息

当我使用此代码通过mailgun发送消息时，它工作正常：

$mg = Mailgun::create('my-key');

$mg->messages()->send('mg.domain.com', [
    'from'    => 'info@domain.com',
    'to'      => 'email@something.com',
    'subject' => 'subject',
    'text'    => 'my text'
]);

但是，当我使用此代码时，会出现一个错误：

$mg = Mailgun::create('my-key');

$mg->messages()->send('mg.domain.com', [
    'from'    => 'info@domain.com',
    'to'      => 'e_mail@something.com', // this line
    'subject' => 'subject',
    'text'    => 'my text'
]);

因此，当我在EmailAddress中使用下划线时，它会抛出一个错误，如下所示：

Uncaught Mailgun\Exception\HttpClientException: The parameters passed to the API were invalid. Check your inputs! in [domain]/vendor/mailgun/mailgun-php/src/Mailgun/Exception/HttpClientException.php:52 
Stack trace: 
#0 [domain]/vendor/mailgun/mailgun-php/src/Mailgun/Api/HttpApi.php(91): Mailgun\Exception\HttpClientException::badRequest(Object(GuzzleHttp\Psr7\Response)) 
#1 [domain]/vendor/mailgun/mailgun-php/src/Mailgun/Api/HttpApi.php(73): Mailgun\Api\HttpApi->handleErrors(Object(GuzzleHttp\Psr7\Response)) 
#2 [domain]/vendor/mailgun/mailgun-php/src/Mailgun/Api/Message.php(52): Mailgun\Api\HttpApi->hydrateResponse(Object(GuzzleHttp\Psr7\Response), 'Mailgun\\Model\\M...') 
#3 [domain]/test.php(15): Mailgun\Api\Message->send('[domain]...', Array) #4 {main} thrown in [domain]/vendor/mailgun/mailgun-php/src/Mailgun/Exception/HttpClientException.php on line 52

我怎样才能解决这个问题？谢谢你的帮助