Having some bad mail server problems

Hi guys,

Could use some help here. We've been having users complain that their email is either bouncing back to them or they get message delayed emails and finally it bounces back. I checked all the usual things like reversedns, blocklists, etc, but it continues to happen. Currently, if I look in the queue I see a few 421 4.2.1 errors and the message keep retrying. We do have two Interner connections here and the mail could go out on both, but the DNS is set up correctly.

Any help would be appreciated! I also ran the Microsoft Remote connection tests and it passed on both IP's:

      Performing Outbound SMTP Test
       The outbound SMTP test was successful.
      Additional Details
Elapsed Time: 19372 ms.
      Test Steps
      Attempting reverse DNS lookup for IP address
       The Microsoft Connectivity Analyzer successfully resolved IP address via reverse DNS lookup.
      Additional Details
      Performing Real-Time Black Hole List (RBL) Test
       Your IP address wasn't found on any of the block lists selected.
      Additional Details
      Test Steps
      Performing Sender ID validation.
       Sender ID validation was performed successfully.
      Additional Details
      Test Steps

Our mail server would be mail.orbuscompany.com

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AmitIT ArchitectCommented:
What is the next hop after Exchange server?
Do you have any email gateway after Exchange server?
Error clearly indicates DNS issue. Are you running Exchange on VM? If yes, check VLAN configuration also.
are your two internet connections in fail over or load balance.  Are the IP addresses for both ISP listed in MX record with the correct priority if they're failover?  You would also probably have to have them configured in the spf record as well for testing remove one of the internet connections (esp if not listed on mx records)
AmitIT ArchitectCommented:
Focus on next hop, sometime ISP changes IP's without updating customer. Ask your ISP.
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OrbusLLCAuthor Commented:
We are using Postini right now as the in between. I have all IP's in the SPF and the circuits are failover using DNS Made Easy.
AmitIT ArchitectCommented:
then focus on postini. restart postini and check again.
OrbusLLCAuthor Commented:
Postini is a spam service in the cloud provided by Google.
AmitIT ArchitectCommented:
then call Google and tell them about this issue you are facing. Before that you can do nslookup for you Exchange server ip's as well. just to check, if DNS records for Exchange server exist properly or not.
OrbusLLCAuthor Commented:
Looks like it has to do with our Sonicwall and DNS. I have the DNS record set for, but the mailserver is showing the IP as which is causing issues. Can someone guide me into making the correct NAT entry on the Sonicwall?
AmitIT ArchitectCommented:
As I said it is a DNS issue. I also mentioned to focus on next hop, which is Sonicwall in your case. For sonic wall create a new question.

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