Exchange Mail Delivery Issue - MSExchangeTransport

its not an exchange eror message but is is caused by external firewall or anti spam software i would say
are you sending email thru your isp?
i would try contact the other domain first and check with them

We currently route our mail through Postini.  Their provider claims they haven't blocked our domain, but being that we use Postini they maybe blocking that IP range as opposed to our domain.

you can enable message tracking
send a few test emails to this domain and see if it gets by postini on the tracking tool which i think this will show(not 100% certain)
it will probably come up with something like "transferred to postini"
setting up an smtp connecter could be another option for this domain only

I have logged into their Postini account and I can see that mail is being delivered to their account, it is still unable to get from Postini to their domain.  I am going to send their host our Postini IP's and see if they are blocking at these IP's.  I'll post what I find.....

try lowering the MTU in exhange to 1404
also repeat thyis on all your routers/firewalls

I've contacted their host's support and they claim that our IP's are not being blocked.  In response to kenny240179, can you explain further as to why this would resolve my issue?

did this just start happening recently?

Yes, it started on Monday.  We've made no changes or updates this week.

The Maximum Transmission Unit (MTU) is the largest size of IP datagram which may be transferred using a specific data link connection The MTU value is a design parameter of a LAN and is a mutually agreed value (i.e. both ends of a link agree to use the same specific value) for most WAN links. The size of MTU may vary greatly between different links (e.g. typically from 128 B up to 10 kB)..

if the mtu size is too high with regard to email the recieving server can time out and cause a bounced response. lowering the mtu will reduce the packet size and limit the amount of data transfered in the shortest possible time. I have seen this happen with older antispam solutions.

Thanks for the details on your recommendation.  I am currently calling Postini and will post any updates to this issue.

check if postini can send an email to them

They are unable to send mail to them.  I am on the phone with tech support as we speak.

I agree, Postini was unable to Telnet to their server from one of their Prod servers.  I can telnet from my end (diff IP) so apparently their Host is the issue.  Thanks for your efforts poweruser32.