如果你读https://sendersupport.olc.protection.outlook.com/pm/troubleshooting.aspx， 它说
Confirm that your DNS is set up correctly
Try connecting to mail.hotmail.com via port 25. If you are unable to connect, then attempt to telnet over port 25 directly to our email servers (MTAs). You can find the current list of our MTAs by querying "nslookup –q=mx hotmail.com" from a command prompt (this should work in a variety of Operating Systems). Currently, the addresses for these servers are mx1.hotmail.com, mx2.hotmail.com, mx3.hotmail.com and mx4.hotmail.com. If that doesn't work, try connecting directly to the IPs. If you are able to connect directly to the IP and not mail.hotmail.com, then it is likely that there is an issue with your DNS server.
那么如何从 DNS 通过端口 25 连接到 mail.hotmail.com？
答案1
这是两个单独的指令...
您需要确认您的 DNS 已设置并正常工作，并且 mail.hotmail.com 可以解析。
例如nslookup mail.hotmail.com，或者 dig mail.hotmail.com甚至 ping mail.hotmail.com应该返回一个 IP 地址，而不会导致未找到主机名的错误或类似的错误。
如果出现这种情况，则需要确认您可以与 mail.hotmail.com 建立到 TCP 端口 25（SMTP 协议用于邮件传递的端口）的连接。您可以使用 telnet 来实现这一点。