我怀疑是因为你没有设置端口，SMTPSecure 应该是小写的.改变这个:

I suspect it's because you've not set the port, and SMTPSecure should be lower case. Change this:

$mail->SMTPSecure = 'tls';
$mail->Port = 587;

除此之外，请检查您的 ISP/防火墙是否允许您发送出站邮件，以及您的 DNS 是否正常工作.

Beyond that, check that you're allowed to send outbound mail by your ISP/firewall and that your DNS is working.