我正在尝试在 Ubuntu 上设置邮件服务器（postfix 和 dovecot）。但是，我无法发送/接收电子邮件，并收到类似错误，如Postfix：在接收初始服务器问候时与 *somehost* 失去连接。我的错误信息如下：
Jan 5 03:46:49 oakwise-12752 postfix/smtp[22531]: 48079C08F4: conversation with gmail-smtp-in.l.google.com[74.125.25.27] timed out while receiving the initial server greeting
当我尝试 telnet 到 google 邮件服务器时，我可以连接到主机，但没有收到问候消息 (220)。像这样：
$ telnet gmail-smtp-in.l.google.com 25
Trying 74.125.25.27...
Connected to gmail-smtp-in.l.google.com.
Escape character is '^]'.
当我尝试 telnet 到我自己的邮件服务器时，我可以成功收到问候消息。
$ telnet localhost 25
Trying 127.0.0.1...
Connected to myhost.mydomain.com
Escape character is '^]'.
220 myhost.mydomain.com ESMTP Postfix (Ubuntu)
你知道我的主机配置是否有问题吗？如果您需要更多信息，请告诉我。
更新
tcpdump以下是while的一些结果telnet gmail-smtp-in.l.google.com 25。
tcpdump host 74.125.25.26
09:20:39.856647 IP myhost.mydomain.com.53742 > fa-in-f26.1e100.net.smtp: Flags [S], seq 2040695833, win 14600, options [mss 1460,sackOK,TS val 274530380 ecr 0,nop,wscale 7], length 0
09:20:40.013693 IP fa-in-f26.1e100.net.smtp > myhost.mydomain.com.53742: Flags [S.], seq 1029741075, ack 2040695834, win 14180, options [mss 1430,sackOK,TS val 128311508 ecr 274530380,nop,wscale 6], length 0
09:20:40.013747 IP myhost.mydomain.com.53742 > fa-in-f26.1e100.net.smtp: Flags [.], ack 1, win 115, options [nop,nop,TS val 274530420 ecr 128311508], length 0
09:20:51.837739 IP myhost.mydomain.com.53727 > fa-in-f26.1e100.net.smtp: Flags [P.], seq 1931780617:1931780622, ack 3676242651, win 115, options [nop,nop,TS val 274533376 ecr 3949456046], length 5
09:22:52.157741 IP myhost.mydomain.com.53727 > fa-in-f26.1e100.net.smtp: Flags [P.], seq 0:5, ack 1, win 115, options [nop,nop,TS val 274563456 ecr 3949456046], length 5
09:24:52.477713 IP myhost.mydomain.com.53727 > fa-in-f26.1e100.net.smtp: Flags [P.], seq 0:5, ack 1, win 115, options [nop,nop,TS val 274593536 ecr 3949456046], length 5
09:26:52.797732 IP myhost.mydomain.com.53727 > fa-in-f26.1e100.net.smtp: Flags [P.], seq 0:5, ack 1, win 115, options [nop,nop,TS val 274623616 ecr 3949456046], length 5
09:28:53.117719 IP myhost.mydomain.com.53727 > fa-in-f26.1e100.net.smtp: Flags [P.], seq 0:5, ack 1, win 115, options [nop,nop,TS val 274653696 ecr 3949456046], length 5
09:30:53.437729 IP myhost.mydomain.com.53727 > fa-in-f26.1e100.net.smtp: Flags [P.], seq 0:5, ack 1, win 115, options [nop,nop,TS val 274683776 ecr 3949456046], length 5
更新2
Google 告诉我，ISP 的日志会阻止端口 25 以防止垃圾邮件。我正在使用公司云提供的虚拟主机。端口 25 是否可能被公司防火墙或 ISP 阻止？我如何确定它是否被阻止了？
答案1
我同意这可能是 Google 使用的反垃圾邮件技术：
以下是来自另一个 IP 的 telnet 输出：
> telnet gmail-smtp-in.l.google.com 25
Trying 173.194.70.26...
Connected to gmail-smtp-in.l.google.com.
Escape character is '^]'.
220 mx.google.com ESMTP j49si145368071eep.45
quit
221 2.0.0 closing connection j49si145368071eep.45
Connection closed by foreign host.
和您提到的 IP 相同的 telnet：
> telnet 74.125.39.27 25
Trying 74.125.39.27...
telnet: connect to address 74.125.39.27: Operation timed out
telnet: Unable to connect to remote host
答案2
这可能是谷歌使用的反垃圾邮件技术。其他 smtp 服务器的行为是否与 google-mx 类似？可能会tcpdump得到一些线索