I now repeatedly see SPAM from a source that has no MX record in their
rDNS domain and they apparently know how to by-pass greylisting.

I decided to follow the example in this mailing list and used telnet
<mailserver> 25 to test my server.


I started with all DNS Tests active and first I got rejected because of
reject-ip-in-cc-rdns which was correct, because

 nslookup <myip>

indeed returns a reverse Domain name with my IP address included and is
from a country domain.


I deactivated reject-ip-in-cc-rdns and did the test again. Now I was
rejected because of reject-unresolvable-rdns. And indeed

 dig <reverse domain> a

fails to respond.


I deactivated reject-unresolvable-rdns and did the test again. Now I was
not rejected any more, but when I do

 dig <reverse domain> mx

it fails to reaspond, meaning there is no mx record. Shouldn't Spamdyke
have rejected it on this basis?


I did the same test from a server that has no country in the domain, but
has not mx record. I noticed that both are subdomains.

My connections address is in the format <ip-address>.static.jazztel.es
When I test

dig jazztel.es mx

indeed it responds. Could it be Spamdyke tests MX of the domain instead
of the subdomain? Is that a wise thing to do, since many ISP will have a
MX in their domain, isn't it?




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