Please fill out the fields below so we can help you better. Note: you must provide your domain name to get help. Domain names for issued certificates are all made public in Certificate Transparency logs (e.g. crt.sh | example.com), so withholding your domain name here does not increase secrecy, but only makes it harder for us to provide help.
My domain is: mail.atx.my
I ran this command:
It produced this output:
My web server is (include version): Server version: Apache/2.2.15 (Unix)
The operating system my web server runs on is (include version):
My hosting provider, if applicable, is:
I can login to a root shell on my machine (yes or no, or I don't know): yes
I'm using a control panel to manage my site (no, or provide the name and version of the control panel): no
The version of my client is (e.g. output of certbot --version or certbot-auto --version if you're using Certbot): no
Your smtp server is serving a self-signed certificate. It has something to do with Fireware HTTPS Proxy (SN D022032560F6E 2017-12-15 01:12:59 GMT) CA (WatchGuard_Technologies).
You have not configured the mail.atx.my service to use a proper certificate (it's using a default one, which is not trusted by other computers).
This usually involves getting a certificate for the correct name via Let's Encrypt (using certbot for instance), then you update configuration of your service to use the correct certificate files and then usually you restart the service so it picks up the correct certificate.
If none of this makes sense to you it's worth doing some research to get up to speed on the topic, or get someone else to do it for you.