Cannot send emails through Cyberpanel webmail

Hi all,

I’m stuck with Cyberpanel web email. I wanted to set-up my own mail server, that I would use to send notifications from my other web server, but the problem I have now is that I cannot send emails. I can receive them.

I have Linux Ubuntu 24.04 LTS, and I’ve bought a domain at namecheap.
I’ve created my custom DNS servers and used them to configure the website and email server.
I’ve created an email account under mine domain, I’ve tested the DNS records for the domain on mxtoolbox[dot]com website, and I get the following error when testing the email server:

SMTP Valid Hostname - Reverse DNS is not a valid Hostname

Connecting to

220 ccdtestadmin[dot]com ESMTP Postfix [319 ms]
EHLO keeper-us-east-1b[dot]mxtoolbox[dot]com
250-SIZE 30720000
250 CHUNKING [231 ms]
MAIL FROM:<supertool@mxtoolboxsmtpdiag[dot]com>
250 2.1.0 Ok [207 ms]
RCPT TO:<test@mxtoolboxsmtpdiag[dot]com>
554 5.7.1 <test@mxtoolboxsmtpdiag[dot]com>: Relay access denied [225 ms]

LookupServer 1525ms
I am able to receive emails, but I cannot send any emails, they are all getting stuck in queue and their status is being set to deferred.

What is causing this issue?

BTW, I used this tutorial to set-up email server, all was fine, except that during the installation of Cyber Panel, I got a warning that my provider (probably referring to Linode) is blocking port 25. So I created a firewall for that Linux VM in Linode and enabled that port (along with following ports: 25, 110, 143, 465, 587, 993)

Can anyone provide assistance?

You need to ask linode unblock port 25 default they block it.

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First thing is port when you have a new account your email ports are blocked and then you have to check mail

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