我有一个新的 VPS，从那时起我就无法发送电子邮件通知。起初，用于出站流量的端口 25 被阻止，现在没问题了。但我的 IP 被添加到黑名单中，原因如下：
CBL Lookup Utility
IP Address xx.xx.xx.xx is listed in the CBL. It shows signs of being
infected with a spam sending trojan, malicious link or some other form of botnet.
It was last detected at 2016-11-08 03:00 GMT (+/- 30 minutes), approximately 10
hours ago.
This IP address is HELO'ing as "localhost.localdomain"
which violates the relevant standards (specifically: RFC5321).
The CBL does not list for RFC violations per-se. This _particular_ behaviour,
however, correlates strongly to spambot infections.
In other words, out of thousands upon thousands of IP
addresses HELO'ing this way, all but a handful are infected
and spewing junk. Even if it isn't an infection, it's a misconfiguration that
should be fixed, because many spam filtering mechanisms
operate with the same rules, and it's best to fix it
regardless of whether the CBL notices it or not.
DO NOT TELNET TO YOUR SERVER TO SEE WHAT IT SAYS.
Telnet will show you the banner, not the HELO."
因此在邮件日志中我有类似这样的内容：
(mxeue002) Nemesis ESMTP Service not available 554-No SMTP service 554-IP
address is black listed. 554 For explanation visit
当我通过 telnet 连接到服务器时，我得到：
Escape character is '^]'.
220 localhost.localdomain ESMTP Postfix
提供商是 1and1。我拥有服务器的完全根控制权。