DomainAcceptsNoMail returned if domain contains an invalid MX record with an empty target

[ValCanBuild]

Looking at a domain like this for example: clarionhg.com

Doing dns_get_record("clarionhg.com", DNS_MX); returns

[
    [
      "host" => "clarionhg.com",
      "class" => "IN",
      "ttl" => 752,
      "type" => "MX",
      "pri" => 10,
      "target" => "clarionhg-com.mail.protection.outlook.com",
    ],
    [
      "host" => "clarionhg.com",
      "class" => "IN",
      "ttl" => 752,
      "type" => "MX",
      "pri" => 10,
      "target" => "",
    ],
  ]

You can see they have a valid MX record (first one) but they also have an invalid one with an empty target. This causes the check in DNSCheckValidation->validateMxRecord to return a DomainAcceptsNoMail error and the whole check to fail.

This is wrong - even though the domain DNS is misconfigured it still contains a valid MX record ( the first one ) so it should pass.