Incoming newsletter emails bouncing

Exchange 2010 on Server 2008 Ent using Exchange built in anti-spam.

I'm having an issue with newsletters not being delivered. I've lowered the spam filter to almost nothing (Resulting in a massive amount of spam) but they're still being blocked.

This is a very big deal to my boss, and I cannot figure it out for the life of me. I've whitelisted the domain - and the domain it's coming from can email us on an individual basis...but the newsletters do not come through.

When the said domain checks their program that sends the newsletters, it shows that the previous attempt bounced and automatically sets them to a disabled status.

This isn't one domain's newsletter - There are multiple.


Has anyone run into anything similar to this before? I can provide any additional information you need. My boss is REALLY on me about this!
RISLAAsked:
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RISLAConnect With a Mentor Author Commented:
This was a problem with our MX records. We had recently added a third party encryption (ZixCorp) and they incorrectly setup a subdomain MX record. Since removing the record, no issues.
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it_saigeDeveloperCommented:
What is the bounce message?

-saige-
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Joshua GrantomSystems AdministratorCommented:
You will probably need to whitelist their mail server IP address, not just the email address. It sounds like whatever is sending their newsletter is on an IP block list. You can receive email from other users on the same domain because it is coming from their mail server and not the server that is sending the newsletter.

This is a common setup to minimize the risk of your main mail server from being blocked as spam.
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RISLAAuthor Commented:
...........
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