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为什么同一目标 smtp 服务器的 nmap 扫描显示端口 25 丢失

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为什么同一目标 smtp 服务器的 nmap 扫描显示端口 25 丢失

我正在新网络上配置新服务器，并努力使出站 SMTP 能够与已知邮件服务器配合使用。

如果我从现有服务器执行 nmap 扫描，则会显示端口 25，但从新服务器则不会显示。

从现有服务器

[user@existing ~]$ nmap -Pn -v smtp-mail.outlook.com --dns-servers 8.8.8.8
Starting Nmap 5.51 ( http://nmap.org ) at 2016-11-08 16:50 GMT
Initiating Parallel DNS resolution of 1 host. at 16:50
Completed Parallel DNS resolution of 1 host. at 16:50, 0.84s elapsed
Initiating Connect Scan at 16:50
Scanning smtp-mail.outlook.com (65.55.176.126) [1000 ports]
Discovered open port 25/tcp on 65.55.176.126
Discovered open port 587/tcp on 65.55.176.126
Completed Connect Scan at 16:50, 7.24s elapsed (1000 total ports)
Nmap scan report for smtp-mail.outlook.com (65.55.176.126)
Host is up (0.078s latency).
Not shown: 998 filtered ports
PORT    STATE SERVICE
25/tcp  open  smtp
587/tcp open  submission

Read data files from: /usr/share/nmap
Nmap done: 1 IP address (1 host up) scanned in 8.11 seconds

从新服务器

[user@new ~]$ nmap -Pn -v smtp-mail.outlook.com --dns-servers 8.8.8.8

Starting Nmap 6.40 ( http://nmap.org ) at 2016-11-08 17:48 GMT
Initiating Parallel DNS resolution of 1 host. at 17:48
Completed Parallel DNS resolution of 1 host. at 17:48, 0.01s elapsed
Initiating Connect Scan at 17:48
Scanning smtp-mail.outlook.com (65.55.176.126) [1000 ports]
Discovered open port 587/tcp on 65.55.176.126
Completed Connect Scan at 17:48, 8.14s elapsed (1000 total ports)
Nmap scan report for smtp-mail.outlook.com (65.55.176.126)
Host is up (0.081s latency).
Not shown: 999 filtered ports
PORT    STATE SERVICE
587/tcp open  submission

Read data files from: /usr/bin/../share/nmap
Nmap done: 1 IP address (1 host up) scanned in 8.19 seconds

主要区别是端口 25 未显示。

据我所知，我没有阻止来自新服务器的任何出站连接。

所以想知道是否有人知道为什么会发生这种情况？

我假设 nmap 正在端口上执行基本连接，并且没有收到响应，但不清楚为什么相同的连接到 587 有效

作为参考，直接端口连接到 587 显示工作

[user@new ~]$ nc -v smtp-mail.outlook.com 587
Ncat: Version 6.40 ( http://nmap.org/ncat )
Ncat: Connected to 65.55.163.152:587.
220 BLU437-SMTP51.smtp.hotmail.com Microsoft ESMTP MAIL Service, Version: 8.0.9200.16384 ready at  Wed, 9 Nov 2016 02:27:36 -0800

至 25

[user@new ~]$ nc -v smtp-mail.outlook.com 25
Ncat: Version 6.40 ( http://nmap.org/ncat )
Ncat: Connection timed out.

答案1

正如@EEAA 所建议的 - 由于其他人的滥用，我们的 ISP 正在阻止出站端口 25 SMTP。

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