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On my home network, I am trying to connect all the devices to the new SMTP (port 25) relay at my new ISP. I can connect to the port from 2 separate machines (laptop via wireless lan, raspberry pi via ethernet), using both sendmail and telnet. The nmap report is as follows:
# nmap rely.wcg.net.au -p 25
Starting Nmap 7.60 ( https://nmap.org ) at 2019-08-19 07:52 AEST
Nmap scan report for rely.wcg.net.au (203.134.11.19)
Host is up (0.021s latency).
rDNS record for 203.134.11.19: 19.11.134.203.sta.m2core.net.au
PORT STATE SERVICE
25/tcp open smtp
Nmap done: 1 IP address (1 host up) scanned in 0.10 seconds
From 2 other devices connected to the same network (Asus router running asusWRT and a fileserver running ubuntu), I cannot connect to this port. The failing nmap is as follow:
# nmap rely.wcg.net.au -p 25
Starting Nmap 7.60 ( https://nmap.org ) at 2019-08-19 07:52 AEST
Nmap scan report for rely.wcg.net.au (203.134.11.19)
Host is up (0.66s latency).
rDNS record for 203.134.11.19: 19.11.134.203.sta.m2core.net.au
PORT STATE SERVICE
25/tcp filtered smtp
Nmap done: 1 IP address (1 host up) scanned in 11.28 seconds
There is something that I do not understand here. Can you suggest the next debugging steps?
Thanks
Thanks for closing the loop on your question. This would have more educational value for readers if you elaborate a little on why. Also, you can accept your own answer in 2 days by clicking the checkmark. That will indicate that it is solved. – fixer1234 – 2019-08-18T23:27:07.027