Emails Randomly Reaching Destination

Vernon Webb logs at
Fri Mar 19 13:05:39 GMT 2010

I have an issue I have been struggling with for some time. I know this might
be a bit off topic here, but figured this would be the best group to ask as
who is more knowledgeable about this kind of stuff than you guys? 


When sending emails out they sometimes reach their destination and sometimes
not. We host our emails with a company called XO that offers a service that
checks for SPAM (I'd rather have a Linux setup with MailScanner etc, but
this is what the client wants) and then relays the email to our Exchange
server.  When sending out emails they go directly from our Exchange server
to its destination. 


One of the thing I've discovered is that the XO email servers has a
clustered server setup and when I use to see if the IPs are
blacklisted  I find that on many occasions they are listed on RBL list
sometimes as many as 3 and 4 times, but sometimes not at all depending on
which server in the clustered rotation is up at the time. I see this as a
problem, however I am being assured that the domain name that I am sending
the email from has nothing to do with whether or not an email reaches its
destination, but rather the IP address. Naturally I have tested the IP
address of our Exchange server and it is not black listed. So my question
is, why would the email reach its destinations only sometimes unless somehow
there is a dnsresolver  involved that is checking the email's actual domain
name as well as the IP address. I'm thinking that this is actually the case
butu I could be wrong.


Anyone have any comments/suggestions on resolving this issue?






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