我无法从我的 PC 连接到 SMTP 服务器。我使用 Debian sid。
telnet mail.example.com 25
Trying 12.23.34.45...
telnet: Unable to connect to remote host: Connection timed out
来自我网络外部的另一台 Debian PC：
telnet mail.example.com 25
Trying 12.23.34.45...
Connected to mail.example.com.
Escape character is '^]'.
220 mail.example.com ESMTP Exim 4.63 Mon, 02 Apr 2012 22:14:09 +0200
ping也永远挂起，当我点击Ctrl+ 时，C它会显示“100% 丢包”。最后，traceroute满是星号：
traceroute mail.example.com
traceroute to mail.example.com (12.23.34.45), 30 hops max, 60 byte packets
1 * * *
2 * * *
3 * …