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. https://crt.sh/?q=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: juwonpi.kro.kr
I ran this command: sudo certbot certonly --standalone -d mail.juwonpi.kro.kr
and it said
Saving debug log to /var/log/letsencrypt/letsencrypt.log
Requesting a certificate for mail.juwonpi.kro.kr
Certbot failed to authenticate some domains (authenticator: standalone). The Certificate Authority reported these problems:
Domain: mail.juwonpi.kro.kr
Type: dns
Detail: no valid A records found for mail.juwonpi.kro.kr; no valid AAAA records found for mail.juwonpi.kro.kr
Hint: The Certificate Authority failed to download the challenge files from the temporary standalone webserver started by Certbot on port 80. Ensure that the listed domains point to this machine and that it can accept inbound connections from the internet.
Some challenges have failed.
Ask for help or search for solutions at https://community.letsencrypt.org. See the logfile /var/log/letsencrypt/letsencrypt.log or re-run Certbot with -v for more details.
It produced this output:
My web server is (include version):
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):
I'm using a control panel to manage my site (no, or provide the name and version of the control panel):
The version of my client is (e.g. output of certbot --version or certbot-auto --version if you're using Certbot):