Hi everybody - I have a question for the DNS and SMTP experts...

Unfortunately if I want your help on this matter I can't really keep much info private.

I am (trying to) run a mail server for a domain which I purchased (mnin.org). I also have
registered a free one (mnin.ods.org). They point to the same IP address and my mail
server will accept messages for either domain. That IP address is dynamic and I know this
complicates things, but set that aside for the moment. Suppose I try to deliver a message
to/through another MTA from my ideal email address (mh@mnin.org):

HELO mnin.org
250 another.mta.com
MAIL FROM: mh@mnin.org
451 4.1.8 Domain of sender address mh@mnin.org does not resolve

OK - A number of servers give me an identical error when I attempt to use mh@mnin.org
as the source address. Now, using a hotmail account or something I try to use mh@mnin.org
as the destination address:

451 mnin.org: Name server timeout
Message could not be delivered for 5 days
Message will be deleted from queue

That is obviously from one particular server but others produce a similar effect - undeliverable
and returned mail. My first guess concerned reverse DNS. Everyone says this is the responsibility
of my ISP, which is fine - no problem. But, if this was the case, then my free domain (mh@mnin.ods.org)
should be problematic as well. Lets see:

HELO mnin.org
250 another.mta.com
MAIL FROM: mh@mnin.ods.org
250 sender OK

No problems. There are also no problems using this address as the destination - messages sent to
it are delivered immediately. In fact, the only trouble whatsoever is sending mail to AOL's servers,
which is because my IP is dynamic.

So with all this considered, what could be the reason I cannot send or receive mail to mh@mnin.org
but I can do both flawlessly with mh@mnin.ods.org??

The two domains obviously have different name servers. There must be something specific one has
that the other doesn't. Something crucial! For starters, I noticed the name servers for mnin.org
do not respond authoritatively and allow recursive lookups; not to mention they received an F
using the time lookup tool on dnsstuff.com. The name servers for mnin.ods.org respond
authoritatively, do not allow recursive lookups, and received in A+ on timing.

If anyone understands this problem or can help me resolve it, please post! Or hell, you can even
email me - but not to mh@mnin.org!

Thank you

-mh