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I’ve never really found an error which google has not at least a few entries covering the error message to some degree. But for a couple of month now I was not able to send a mail from batland.de to a specific mail server, because the mail was always rejected by the postmaster of this particular server, because of this:
Blocked because of fully generic DNS (#5.7.1)
Google came up with zero entries which quote this error message. And at first I had no clue what a fully generic DNS is. So I just decided to not sent mails to this server via batland.de! Yesterday, for some unknown reason I definitely wanted to fix this issue. I thought back to my college time when I had a lecture on SPAM and how to fight spam.
On simple way to fight phishing mails and spam in general is to only accept mails from a mail server, if this mail server is authorized to sent mails for this domain. So a trivial approach is to check, if a mail sent from mail server yx.com belongs to this domain. Therefore, the recipient mail server just checks this by doing a reverse DNS query on the IP. This is a in a nutshell description of the Sender Policy Framework (SPF) with some simplifications. So I checked on the reverse DNS name of my IP and, guess what, it does not resolve to batland.de, but a different domain because several domains run on this IP. So I changed the reverse dns entry to batland.de and after a while (because of the caching) it just worked.
So anyone else stumbling over this error has some information on where to look for a solution to this problem. In the next days I need to take a closer look at the dns entries regarding SPF so that all domains on this IP can sent mails to a mail server which uses SPF.
Bye,Dennis
Posted by: admin