<?php
use Microsoft\Graph\GraphServiceClient;
use Microsoft\Graph\Generated\Users\Item\SendMail\SendMailPostRequestBody;
use Microsoft\Graph\Generated\Models\Message;
use Microsoft\Graph\Generated\Models\ItemBody;
use Microsoft\Graph\Generated\Models\BodyType;
use Microsoft\Graph\Generated\Models\Recipient;
use Microsoft\Graph\Generated\Models\EmailAddress;
use Microsoft\Graph\Generated\Models\InternetMessageHeader;
$graphServiceClient = new GraphServiceClient($tokenRequestContext, $scopes);
$requestBody = new SendMailPostRequestBody();
$message = new Message();
$message->setSubject('9/9/2018: concert');
$messageBody = new ItemBody();
$messageBody->setContentType(new BodyType('hTML'));
$messageBody->setContent('The group represents Nevada.');
$message->setBody($messageBody);
$toRecipientsRecipient1 = new Recipient();
$toRecipientsRecipient1EmailAddress = new EmailAddress();
$toRecipientsRecipient1EmailAddress->setAddress('AlexW@contoso.com');
$toRecipientsRecipient1->setEmailAddress($toRecipientsRecipient1EmailAddress);
$toRecipientsArray []= $toRecipientsRecipient1;
$message->setToRecipients($toRecipientsArray);
$internetMessageHeadersInternetMessageHeader1 = new InternetMessageHeader();
$internetMessageHeadersInternetMessageHeader1->setName('x-custom-header-group-name');
$internetMessageHeadersInternetMessageHeader1->setValue('Nevada');
$internetMessageHeadersArray []= $internetMessageHeadersInternetMessageHeader1;
$internetMessageHeadersInternetMessageHeader2 = new InternetMessageHeader();
$internetMessageHeadersInternetMessageHeader2->setName('x-custom-header-group-id');
$internetMessageHeadersInternetMessageHeader2->setValue('NV001');
$internetMessageHeadersArray []= $internetMessageHeadersInternetMessageHeader2;
$message->setInternetMessageHeaders($internetMessageHeadersArray);
$requestBody->setMessage($message);
$graphServiceClient->me()->sendMail()->post($requestBody)->wait();