Doesn't work for localhost

[Binyamin Laukstein]

On "Step 4: Verify Ownership"

Error: Domain challenge failed.
Please start back at Step 1.

{
  "type": "http-01",
  "status": "invalid",
  "error": {
    "type": "urn:acme:error:connection",
    "detail": "DNS problem: NXDOMAIN looking up A for localhost"
  },
  "uri": "https://acme-v01.api.letsencrypt.org/acme/challenge/eWE0XfjoV-k3svPLgT1anrvILA4lMJ81DuLlU13hAGA/15437867",
  "token": "0GqKsde7_VxV5LuvK3yZTmf2dyA0ZcrcXni3KI5whMw",
  "keyAuthorization": "0GqKsde7_VxV2LuvK3yZTmf2daA0ZcrcXni3KI6whMw.yLc6R0-fPTsTXQMzn6JWWUvsiWulYCbn1rdoMY2wdQU",
  "validationRecord": [{
    "url": "http://localhost/.well-known/acme-challenge/0GqKsde7_VxV1LuvK3yZTmf2dyA0ZcrcXni3KI5whMw",
    "hostname": "localhost",
    "port": "80",
    "addressesResolved": null,
    "addressUsed": ""
  }]
}

[Licaon_Kter]

It should be an internet facing machine with a valid domain name, I'm not sure localhost qualifies for this.

[rugk]

I think Let's Encrypt is a bit stubborn at issuing certs for localhost. They also don't do this for lololololollo.ololol and www.*. That's a pity!
Probably you should try whether 127.0.0.1 works.

[Daniel Roesler]

Let's Encrypt looks up the MX record of the account domain before issuing. It doesn't email it (until you're cert is about to expire), but you still need to have the MX records in your DNS.