更新：2022 年 5 月

所以我在这个问题上苦苦挣扎。对于具有 Exchange Online 和 Microsoft 管理中心访问权限的企业帐户，我可以提供此问题的答案。

TLDR：转到管理中心并选择您要发送邮件的用户。然后在设置“经过身份验证的 SMTP”之后查看“电子邮件”和“电子邮件应用程序”后的设置，只需启用它即可。

仍然无法工作？我已经为您提供了帮助，这就是我如何让它完全发挥作用。

1. 使用PHP Composer，实际上节省了很多工作。
2. 将您的代码替换为我的代码，并在测试后更改

SMTPDebug = SMTP::DEBUG_off;

//SMTP
$mail = new PHPMailer(true); //important
$mail->CharSet = 'UTF-8';  //not important
$mail->isSMTP(); //important
$mail->Host = 'smtp.office365.com'; //important
$mail->Port       = 587; //important
$mail->SMTPSecure = 'tls'; //important
$mail->SMTPAuth   = true; //important, your IP get banned if not using this

//Auth
$mail->Username = 'yourname@mail.org';
$mail->Password = 'your APP password';//Steps mentioned in last are to create App password

//Set who the message is to be sent from, you need permission to that email as 'send as'
$mail->SetFrom('hosting@mail.org', 'Hosting Group Inc.'); //you need "send to" permission on that account, if dont use yourname@mail.org

//Set an alternative reply-to address
$mail->addReplyTo('no-reply@mail.com', 'First Last');

//Set who the message is to be sent to
$mail->addAddress('customer@othermail.com', 'SIMON MÜLLER');
//Set the subject line
$mail->Subject = 'PHPMailer SMTP test';
//Read an HTML message body from an external file, convert referenced images to embedded,
//convert HTML into a basic plain-text alternative body
$mail->msgHTML(file_get_contents('replace-with-file.html'), __DIR__);  //you can also use $mail->Body = "This is a body message in html" 
//Replace the plain text body with one created manually
$mail->AltBody = 'This is a plain-text message body';
//Attach an image file
//$mail->addAttachment('../../../images/phpmailer_mini.png');

//send the message, check for errors
if (!$mail->send()) {
    echo 'Mailer Error: ' . $mail->ErrorInfo;
} else {
}

3. 这可能看起来像您的文件，没关系，但现在是简单棘手的部分。与 Google 一样，Microsoft 也为 SMTP 实现了“开关”。只需从您的企业帐户转到您的管理中心，或者请有权限的人执行该部分操作即可：

@nitin 的代码对我不起作用，因为它在 SMTPSecure 参数中缺少“tls”。

这是一个工作版本。我还添加了两行注释掉的行，您可以在出现问题时使用它们。

isSMTP();
$mail->Host = 'smtp.office365.com';
$mail->Port       = 587;
$mail->SMTPSecure = 'tls';
$mail->SMTPAuth   = true;
$mail->Username = 'somebody@somewhere.com';
$mail->Password = 'YourPassword';
$mail->SetFrom('somebody@somewhere.com', 'FromEmail');
$mail->addAddress('recipient@domain.com', 'ToEmail');
//$mail->SMTPDebug  = 3;
//$mail->Debugoutput = function($str, $level) {echo "debug level $level; message: $str";}; //$mail->Debugoutput = 'echo';
$mail->IsHTML(true);

$mail->Subject = 'Here is the subject';
$mail->Body    = 'This is the HTML message body in bold!';
$mail->AltBody = 'This is the body in plain text for non-HTML mail clients';

if(!$mail->send()) {
    echo 'Message could not be sent.';
    echo 'Mailer Error: ' . $mail->ErrorInfo;
} else {
    echo 'Message has been sent';
}