Could not deliver the message in the time limit specified.

For some reason, when certain people try to send us email to our domain, they get a bounce back. There are very few that actually are having this problem.
mail.parasec.com is one mail server that cannot send to us. AOL, GMail, and hotmail can all send fine to our domain.
Our domain name is mail.montanacorporate.com. I have run a dnsstuff.com DNS report, and everthing comes back with a pass. I have a reverse PTR record setup. I had a SPF record setup, but deleted it to make sure it was not causing a problem. I have made sure the banner on my Exchange server reads mail.montanacorporate.com. I have made sure we have both a mx record and a host record. the mx is setup with a priority of 10 and there is only one.

I have also made sure that there is nothing checked on the smtp server like apply sender id, or  apply inteligent message filter. All are unchecked.

There is no AV installed on the server.

I have no idea what to do to get this fixed.
jrking1978Asked:
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jrking1978Connect With a Mentor Author Commented:
I changed the MTU size on my server to 1300 in the registry. I also did a firmware upgrade on my router. Everything is notw working. I believe it is the MTU setting that did it. When I get some time next week, I am going to reset the MTU size to default on my server and see if emails come thru. I am guessing this is an issue with the Intel nic on the server.
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GWMerrellCommented:
Do you have a copy of the bounce message, that we might be able to know more as to why it is bouncing?
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jrking1978Author Commented:
Your message did not reach some or all of the intended recipients.
      Subject:  TEST E-MAIL
      Sent:     3/6/2009 10:21 AM
The following recipient(s) could not be reached:
      xxxxx@Montanacorporate.com on 3/6/2009 8:38 PM
            Could not deliver the message in the time limit specified.  Please retry or contact your administrator.
            <mail.parasec.com #4.4.7>
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GWMerrellCommented:
I take it that you cannot reproduce the issue, correct?
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jrking1978Author Commented:
I can, if I ask them to send a test email. But I think it may take a bit to get a bounce. I am waiting on a reply from the IT guy at parasec.
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GWMerrellCommented:
Can you repro this outside of thier mail services? I am thinking the problem is on thier END and not yours.
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jrking1978Author Commented:
We also have a 1-800 number that sends us the voicemails left to our email. And it also does not make it thru. But does make it to our gmail account.
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GWMerrellCommented:
Do you have any mail spam/ virus solution services or appliances?
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jrking1978Author Commented:
No, we have a DSL router, hooked to a switch, and then the Exhcange mail server is also hooked ot the same switch. Nothing is before it. Port 25, and 443 are forwaded thru the router to the internal ip address of the Exhcange server.
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jrking1978Author Commented:
Here are some screenshots from our DSL router
firewall.jpg
portfowarding.jpg
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GWMerrellCommented:
That is a pretty clean connection to the outside world. That said, the only thing I can think of is if the router isn't being consistent. When was the last time you power cycled the router?
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jrking1978Author Commented:
I am not sure, I will find out.

It is very consistent with parasec.com, and the voicemail. and i am pretty sure he has rebooted the dwsl router, but I will asl
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jrking1978Author Commented:
We have power sycled the router and it is still giving us problems. I have had the guy ata parasec try a telnet to port 25 and it works and does not ahve a problem.
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GWMerrellCommented:
Are we certain these are legitimate bounce messages and not spam. Sounds to me as if everything is configured and running as it should.
Do advise when you get a moment.
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jrking1978Author Commented:
Yes they are legitimate messages being sent by the IT guy at parasec. Could it be somthing with esmtp? I have no idea how that works, but saw some articles about that.
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jrking1978Author Commented:
Would I need to forward UDP traffic in?
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GWMerrellCommented:
No, that shouldn't be required.  I am out of suggestions, let me research some more.
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jrking1978Author Commented:
I made a discovery. I enabled some logging on the SMTP server and found this. This is a domain we cannot recieve from:

2009-04-17 21:33:10 64.6.42.72 DC1 192.168.0.100 0 TIMEOUT 121 1210713664 84 4 644328 SMTP

So we are getting a timeout on the SMTP server. That means it is making it in. Where do I go from here? Re-install SMTP server?
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jrking1978Author Commented:
I used wireshark to sniff the traffic. The SMTP server is recieving all the command until the chunking command. I followed some steps and disabled chunking. I then watched the traffic and it went fine until the data command, then just hung and timed out. I think its a MTU sizing issue and my router, I have asked my clients to contact qwest and order an actiontec router to replace the qwest router. I will come back and post the results of what we find out. If the actiontec router does not work, I am planing on making some adjustments on the MTUS packet size.
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GWMerrellCommented:
Sounds good.
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GWMerrellCommented:
Keep us appraised when you make your change. :)
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