Emails Randomly Reaching Destination

Glenn Steen glenn.steen at
Fri Mar 19 13:37:00 GMT 2010

On 19 March 2010 14:05, Vernon Webb <logs at> wrote:
> 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?
> Thanks
> ~V
I'd skip trying for a "general solution", and instead look at the
specific messages gone missing. What if anything, is common among
them? Can you identify any specifics about the sent messages (like
type of attachments etc)? If you simulate an MTA, using telnet on port
25 to one of the parties that have dropped your mail, what kind of
responses do you see? Are any/all of the "droppers" other Exchange
servers (If M-Sexchange "detect" another M-Sexchange server... they
just might stop talking ESMTP... Urgh!)?
I wouldn't let Exchange talk directly to the internet... Use a
smarthost and something sensible in between... That way you'd at least
get some logs to look at:-).

-- Glenn
email: glenn < dot > steen < at > gmail < dot > com
work: glenn < dot > steen < at > ap1 < dot > se

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