Issue Port 587 is open in Firewall and Telnet but Plesk alert says it's blocked

[bekway]

In our server Mail settings we get "You cannot send emails from Plesk because outbound connections on TCP port 587 is blocked. Check the firewall settings or contact your hosting provider.". Port 587 is open when tested using Telnet, Emails can be sent from port 587 and we even opened it up specifcally in Firewall (not sure this was necessary but we did it anyway). Why do we get this alert?

 

[Brujo]

please check via panel.ini extension or CLI /usr/local/psa/admin/conf/panel.ini what is configured for unavailableMailPorts, unavailableMailPortsHost , unavailableMailPortsList and so on... and test if you can reach it

 

[bekway]

/usr/local/psa/admin/conf/panel.ini just says:
[navigation]
limits.subscriptions = 500

 

[Brujo]

perhaps you have a different plesk edition as I
I just checked it with the extension Panel.ini Editor and on my Systems it looks like:

 

[bekway]

OK I see now, and you are right the ports appear blocked, my settings are almost the same. But how do we explain the "blocked" alert in Plesk panel and, stranglely, why is smtp.gmail.com appearing here?

 

[Brujo]

Unfortunately there is no detailed documentation about this. But I think Plesk is using smtp.gmail.com to test if the defined ports 25 & 587 are open to the outside world. So you should test from your system if you can reach it via telnet on port 587, alternatively they can probably be adjusted. In fact, when I got the error message that outgoing port 587 was blocked on the firewall, and it went away as soon as I configured it right on the firewall

 

[bekway]

I already tested my system and I can reach port 587 via telnet, this is the first thing I tried. And I added port 587 in the Plesk firewall. But the mail settings page still shows the alert message saying its blocked.

 

[Brujo]

whats the output when you do this from your System
# telnet smtp.gmail.com 587

get it connected?

 

[bekway]

telnet smtp.gmail.com 587
Trying 2a00:1450:400c:c07::6c...
telnet: connect to address 2a00:1450:400c:c07::6c: No route to host
Trying 173.194.76.108...
Connected to smtp.gmail.com.
Escape character is '^]'.
220 smtp.gmail.com ESMTP s139sm10136236wme.35 - gsmtp

 

[Brujo]

ok seems to work at least with IPv4, perhaps it has to do with

No route to host

see: IPv6 traffic doesn't work anymore after set System policy for outgoing traffic to Deny: No route to host.

 

[Brujo]

thats all I found about it yet in the changelogs:

Plesk now automatically checks whether the SMTP ports 25 and 587 used for sending mail are filtered. If they are, notifications are shown in the Plesk interface (in “Tools & Settings” > “Mail Server Settings” > “Settings” and “Subscriptions” > “Mail” tab > “Mail Settings”).
If Plesk detects such an infrastructural problem it will recommend possible ways to resolve the issue. (This improvement is available for all Plesk Onyx and Plesk Obsidian versions)

As a workaround until you figured out the real issue: you can try to set in the panel.ini the

[ext-notifier]

unavailableMailPorts

true

to false, this should hide the message. But in general thats helpful to get such an warning if something works not as expected.

 

[DRY411S]

If your PLESK server it hosted on GCP (and perhaps other Cloud providers) you cannot run a mail server of your PLESK server. GCP does not permit you to run mail servers on their VMs. Could this be the reason?