proofpoint issue

We are somewhat new to Proofpoint and an issue started last week that I can't figure out how to address.  One of our users sends emails back and forth with somebody he does business with.  Starting last week, email exchanges between the two sides are getting blocked as spam.  I was able to fix inbound emails with the whitelist but I haven't been able to figure out how to address outbound emails from our side that are getting quarantined as spam.  

How do you figure out why outbound emails are being blocked and then fix the issue?  Thanks in advance.
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Joe SpradlinIT ManagerCommented:
If you host your own (even if you don't) email make sure and check that you are not black listed, which could possibly prevent outbound emails from arriving at their destination(s).
cames01Author Commented:
I had checked on that and we are not blacklisted.  Also, it is only that one email domain that Proofpoint flags as spam when the user tries to email different addresses at that business.  He can email anybody else just fine.
Joe SpradlinIT ManagerCommented:
If that is the case, then how much "tuning" have you done on the Spam detection?  Has anyone tinkered around with tuning the spam detection?  Have you tried disabling the spam filter temporary and see if you can send outbound successfully?

Also, if you just started using Proofpoint, you may be better off contacting their support any verify that you didn't get a botched signature file for spam detection.

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David FavorLinux/LXD/WordPress/Hosting SavantCommented:
Look through my comments in + ensure you have all your infrastructure setup correctly.

If you're using a relay service (like MailGun), likely they'll have a DNS tester to verify all records are correct.

If you're running a native MTA (shudder), you'll have to go through my checklist in the above link + verify all is correct.
cames01Author Commented:
First off, thanks for the responses that my question received.  It turns out that the domain that our user was trying to email was blocked globally by Proofpoint.  Strangely, the domain is not on any black lists that I can find.  So, I don't know what Proofpoint uses for global blocks.  

Proofpoint is looking into removing the domain from the master block list.  Not sure if they will or not.
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