Does cPanel DNSOnly block outgoing emails by default?
Hi friends!,
I have 3 servers running AlmaLinux 9, cPanel DNSOnly, and CSF that are not sending emails (for example, CSF should send a notification when someone logs in via SSH).
As far as I can tell, everything is configured correctly:
1. Port 25 is open in CSF
2. Exim is running properly
3. Added "root: email@domain.com" to "/etc/aliases"
4. Etc.
With the same kind of configuration on other servers that only run AlmaLinux 9 and CSF (using Postfix + Mailx), everything works fine. However, after installing cPanel DNSOnly (which uses Exim), even the most basic tests fail:
echo "My message" | mail -s "My subject" email@example.com
My question is: does cPanel DNSOnly block outgoing email by default because it is a limited version of the software, or is there some specific configuration that must be enabled? Has anyone experienced the same issue?
Thank you very much, and have a great day!
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What do you see in /var/log/exim_mainlog when you send that test message?
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Hi friend!,
I ran the test again:
echo "My message" | mail -s "My subject" email@receiving-server.comThis is the information generated in /var/log/exim_mainlog:
2026-06-14 19:31:18 cwd=/var/spool/exim 3 args: /usr/sbin/exim -Mc 1wYog2-00000003Dp9-09i7
2026-06-14 19:31:18 1wYog2-00000003Dp9-09i7 Sender identification U=mailnull D=-system- S=mailnull
2026-06-14 19:31:18 1wYog2-00000003Dp9-09i7 [DESTINATION_SERVER_IP] SSL verify error: certificate name mismatch: DN="/CN=server1.DESTINATION-SERVER-DOMAIN.com" H="DESTINATION-SERVER-DOMAIN.com"
2026-06-14 19:31:18 1wYog2-00000003Dp9-09i7 ** DESTINATION-EMAIL@DESTINATION-SERVER-DOMAIN.com <root@subdomain.SENDER-SERVER-DNSONLY.net> R=dkim_lookuphost T=dkim_remote_smtp H=DESTINATION-SERVER-DOMAIN.com [DESTINATION_SERVER_IP] X=TLS1.2:ECDHE-RSA-AES256-GCM-SHA384:256 CV=no : SMTP error from remote mail server after pipelined MAIL FROM:<> SIZE=3299: 550 "REJECTED - Bad HELO - Host impersonating [subdomain.SENDER-SERVER-DNSONLY.net]"
2026-06-14 19:31:18 1wYog2-00000003Dp9-09i7 Frozen (delivery error message)
I tried adding the cPanel DNSOnly IP on the receiving server under: Destination WHM/cPanel -> Exim Configuration -> Manager -> Trusted SMTP IP addresses: https://support.cpanel.net/hc/en-us/articles/360055421013-How-to-whitelist-an-IP-address-in-EximHowever, it did not solve the problem.
Thank you very much. Have a nice day!
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No, DNSOnly still sends server notifications so outbound email is not blocked.
Your error message also indicates the mail is leaving the server since the error is coming from the remote host.
What specifically are you trying to do on that system where you need to manually send an email?
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Hi cPRex,
My intention is not to send an email manually; this is only a test to identify the error.
The real issue is that: I am not receiving any notifications from three servers running cPanel DNSOnly. For example, I should receive a CSF notification whenever someone connects via SSH, but those notifications are not arriving.
Perhaps these emails are being detected as spam and rejected. I am running some additional tests to investigate this possibility.
If you have any ideas or can suggest any tests I should perform, please let me know.
Thank you very much for all your help. Have a nice day.
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Here is what the alert from CSF looks like inside /var/log/exim_mainlog:
2026-06-15 11:31:37 1wZ9Hl-00000005Hcq-0EWn <= root@host.hostname.com U=root P=local S=833 T="lfd on host.hostname.com: WHM/cPanel root access alert from x.x.x.x (PA/Panama/-)" for root
so I'd recommend looking through your logs for s similar event there. If there's an issue sending the message you should see it in the main /var/log/exim_mainlog log file.
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