SOLVED Telnet host 25 - no route to host

Tanner1pl

Registered
Dec 17, 2016
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Poland
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Root Administrator
I have basic VM (xenserver installed on dedicated machine) with cPanel on CentOs 6.8, exim 4.87 - nothing fancy. For 2 weeks I am having issue with sending e-mails - it is not global, affects about 10% outgoing emails, random domains, as it is online store. cPanel says "no route to host". I took one of them, lets say [email protected]. In exim logs I saw it matches mail.host.com and gets "no route to host" error. I did some tests:

ping mail.host.com - that works good (so it is not dns issue)

telnet mail.host.com 25 - resolves ip address but shows 'no route to host'

Then I tried telnet from XenServer (host of that VM) and it works good so it is not any ISP or ovh firewall. Something blocks that inside my VM.

I've tried "service iptables stop" and also completely disabled csf and lfd in cPanel - nothing helped.

Do you have any idea what else could I check? I struggle with that for a week and I stuck...
 

cPanelMichael

Administrator
Staff member
Apr 11, 2011
47,903
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telnet mail.host.com 25 - resolves ip address but shows 'no route to host'
Hello,

It's possible the remote mail server is blocking connections from the cPanel server's IP address over port 25. Try contacting the administrator of that remote mail server to see if that's the case.

Thank you.
 

Tanner1pl

Registered
Dec 17, 2016
2
0
1
Poland
cPanel Access Level
Root Administrator
Hello,

It's possible the remote mail server is blocking connections from the cPanel server's IP address over port 25. Try contacting the administrator of that remote mail server to see if that's the case.

Thank you.
Hmm, I would say the same, but the thing is that it is not about just one recipient, issue started one day and affects like 20 totally different hosts.

For all of them I can run telnet mail.host.com 22 (then I see ssh client's hello message) but I can't do that on port 25 - no route to host.
What is weird - now I can't do port 25 from xenserver too, but it still works well from every machine outside OVH which I tested. I've just started to believe that it is their firewall issue...
 

cPanelMichael

Administrator
Staff member
Apr 11, 2011
47,903
2,237
463
What is weird - now I can't do port 25 from xenserver too, but it still works well from every machine outside OVH which I tested. I've just started to believe that it is their firewall issue...
I recommend reaching out to their support team again to verify if there's anything filtering port 25 traffic in their router or firewall rules. While I don't believe it's a port they block by default, searching "OVH Port 25" suggests they might block port 25 in instances where they receive SPAM reports.

Thank you.