Emails not sending to some external email addresses.

I just installed Exchange 2010 and have moved mailboxes, got all of my certificates working correctly.  But one issue has popped up and I can get a handle on it.  Some external sites are not accepting our email and is sending NDR's back to the user.  I am not seeing any error message, but it just says that the message expired.  The interesting part is that this is only happening with certain sites and until those users contact me, I don't know which sites.  

How can I fix this issue?

I wanted to add that I have 2 Exchange Servers with 2 different external IP's in my DNS.  I MX record so both servers can go through our Barracuda for email delivery.
SalongeAsked:
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Tony GiangrecoCommented:
Check the NDR code and see how it relates to your situation. From the exchange server that can't reach the domains, ping and tracert those servers and mailservers to see if you can reach them.
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SalongeAuthor Commented:
The NDR messages just says queue failed.  I ran a trace rt on 3 of the sites and get destination not reachable, but this is after it connected to their domain.  It appears to go through 3 or 4 hops on the domain and then the destination is not reachable.
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Tony GiangrecoCommented:
On the server that can't reach the destination, check it's public IP at mxtollbox.com for a blacklisted situation.
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SalongeAuthor Commented:
we are not on the blacklist.  This is strange because this only happened after the installation of 2010.  I looked at the properties of one of the messages in queue viewer and in the Source IP it has 255.255.255.255 - a 2010 mailbox and one from a 2003 mailbox, it has the internal IP of that Exchange server.  So is this problem with us or the domains we are trying to connect to?
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SalongeAuthor Commented:
Oh the source IP shouldn't make a difference, because I just checked the properties of a message that sent successfully and it had the same source IP listed.
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SalongeAuthor Commented:
Also I did a STMP test in mxtoolbox.com and it told me that my reverse DNS does not contain the hostname.  It says I need to set up a reverse (PTR) record.  How do I do that?
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Tony GiangrecoCommented:
Contact your ISP and have them create a PTR record on your IP.
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Tony GiangrecoCommented:
Some servers won't accept mail without a PTR record on the sending side.
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SalongeAuthor Commented:
Is that done on my external DNS?  If so, I have access to that.
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Tony GiangrecoCommented:
You can try, but normally your ISP has to create the PTR record.
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SalongeAuthor Commented:
okay, thank you.  I will contact them and let you know if this works.  Thanks again for your help.
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SalongeAuthor Commented:
I just checked in my internal DNS and there is a ptr record for my new Exchange Server, so what is next?
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Simon Butler (Sembee)ConsultantCommented:
The PTR on the internal DNS is useless.
You MUST get your ISP to set a PTR on the IP address for you. This is not something that you can do yourself unless they have provided a portal for it. It will specifically say it is for PTR or Reverse DNS.

Simon.
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SalongeAuthor Commented:
Ok thanks
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