更新：2022 年 5 月

所以我對這個問題苦苦掙扎。對於具有 Exchange Online 和 Microsoft 管理中心存取權限的企業帳戶，我可以提供此問題的答案。

TLDR：前往管理中心並選擇您要傳送郵件的使用者。然後在設置“經過身份驗證的 SMTP”之後查看“電子郵件”和“電子郵件應用程式”後的設置，只需啟用它即可。

仍然無法工作？我已經為您提供了幫助，這就是我如何讓它完全發揮作用。

1. 使用PHP Composer，實際上節省了很多工作。
2. 將您的程式碼替換為我的程式碼，並在測試後更改

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 = '[email protected]';
$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('[email protected]', 'Hosting Group Inc.'); //you need "send to" permission on that account, if dont use [email protected]

//Set an alternative reply-to address
$mail->addReplyTo('[email protected]', 'First Last');

//Set who the message is to be sent to
$mail->addAddress('[email protected]', '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. 這可能看起來像您的文件，沒關係，但現在是簡單棘手的部分。與 Google 一樣，Microsoft 也為 SMTP 實作了「開關」。只需從您的企業帳戶前往您的管理中心，或請有權限的人執行該部分操作即可：

@nitin 的程式碼對我來說不起作用，因為它在 SMTPSecure 參數中缺少「tls」。

這是一個工作版本。我還添加了兩行註解掉的行，您可以在出現問題時使用它們。

isSMTP();
$mail->Host = 'smtp.office365.com';
$mail->Port       = 587;
$mail->SMTPSecure = 'tls';
$mail->SMTPAuth   = true;
$mail->Username = '[email protected]';
$mail->Password = 'YourPassword';
$mail->SetFrom('[email protected]', 'FromEmail');
$mail->addAddress('[email protected]', 'ToEmail');
//$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';
}