Domain check / SPF
<SPF>Sender Policy Framework
SPF checks whether an email really comes from a server that is allowed to send on behalf of your domain. Does it check out? Then your message goes through. Does it not? Then the recipient stops the misuse. That way you prevent others from using your domain name, and your own emails arrive more reliably.
<how it should be>
SPF in order
- There is exactly one SPF record on your domain.
- The record ends with -all (strict) or ~all (lenient).
- There are no more than ten DNS lookups, such as include:.