这主要是由于您的托管服务提供商的防火墙问题.看到下面的链接，那里有人遇到类似的问题-

This is mostly due to your hosting providers firewall issues. See on below link where someone had similar issue -

https://github.com/PHPMailer/PHPMailer/issues/295

联系您的托管服务提供商，他们将能够为您提供帮助

Contact your hosting provider, they will be able to help you