42 is one of the wrong answers if you are dealing with spam. SPF, which means Sender Policy Framework seems to be a better solution. SPF is a list of authorized mail sending hosts for your domain. But how does it work?

The implementation takes place at your nameserver by adding a TXT entry to an existing domain. The format is simple:

mydomain.com. IN TXT “resulting spf line”

In my case it looks like that:

stargazer.at IN TXT “v=spf1 mx a:mail.stargazer.at -all”

The mailserver receiving messages from your domain is now able to verify if the mail is sent by an authorized host.