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I am currently trying to set up an email server, and recently stumbled over getting a SSL certificate from Let's Encrypt in this question and realizing it isn't necessary if I don't have a web server, and from the accepted answerer's advice can instead use sudo certbot certonly --standalone -d mail.example.com if I don't have one. I ran into a second problem, and was encouraged by the answerer to create a separate question for it as it is a separate issue.

I tried sudo certbot certonly --standalone -d mail.example.com putting in my own mail subdomain and have seemed to have opened another can of worms:

   Detail: No valid IP addresses found for mail.[my domain name]

This is a bit confusing. Perhaps I have set my MX record wrong? I will list out my DNS records (I've blacked out my droplet's IP address and domain name as I have no clue if it is safe or not to share these things over the internet. If they are necessary to include and it's safe I have no problem unredacting this):

My droplet's DNS records

Here, the redacted bits in the 'Value' column all hide by droplet's IP address and the redacted bits in hostname hide my domain url. It seems to me I have the sufficient records needed to make a connection. I have an A-record pointing domain name to droplet IP address, and I have an MX record that points my mail subdomain to my droplet IP address. Unless I'm mistaken (which I suppose I must be), this should be enough for a mail server.

sangstar
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  • For `certbot --standalone to work` (using a HTTP challenge), your `mail.[your domain]` must have an A (or AAAA, or CNAME directing to A or AAAA) record, and in the end it should be the machine where you run certbot. It doesn't matter if you don't need it for anything else, it's needed for just HTTP challenge. There are other challegnes which possibly don't require that, like dns rfc2136 challenge. – Nikita Kipriyanov Jan 19 '21 at 18:02
  • @NikitaKipriyanov Is this to say that I need an A record for mail.[my domain]? I already have an MX record, and thought this was sufficient. – sangstar Jan 20 '21 at 01:51

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