I am configuring a new server, on a new network and struggling to get outbound SMTP to work to known mail servers.
If I do an nmap scan from my existing server - port 25 shows up, but from my new server it doesn't.
From existing server
[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
From new server
[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
Key difference being port 25 not showing.
AFAIK I am not blocking any outbound connections from new server.
So wondering if anyone has ideas on why this may be happening?
I'm presuming that nmap is performing a basic connect on the port and the response from this is not received back, but unclear why same connect to 587 works
For reference direct port connect to 587 showing working
[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
and to 25
[user@new ~]$ nc -v smtp-mail.outlook.com 25
Ncat: Version 6.40 ( http://nmap.org/ncat )
Ncat: Connection timed out.
