hello I am a beginner and this is the first time I use certbot! the problem is that my postfix mail listens on lel port 587 but my mail client cannot accept the STMP port 587 .. so I will try to create a certificate for my local domain which I created in the powerdns database . but I have the error 'Challenge failed for domain ns1.test.com'
But you don't need to buy a domain.; there are at least a couple of other possibilities:
You could register for a free domain from freenom.com--last I used them, their renewal requirements were annoying, but they were still no-cost domain names.
You may be able to use a free subdomain from a dynamic DNS provider.
You could even run your own PKI. It's pretty straightforward to set up your own Certificate Authority on a Raspberry Pi, which would then be used by devices on your local network. You'd need to install its root certificate on any devices you wanted to trust it, of course, but it works well, and even presents a ACME interface for other systems to get certs: Build a Tiny Certificate Authority For Your Homelab