550 Error Bounce Backs

We are experiencing a high volume of 550 bounce backs to email addresses known to be correct and available.

Here is the email bounce back message:

Diagnostic information for administrators:

Generating server: arlexch01.staff.cci-training.com

Requested #550 Requested action not taken: mailbox unavailable ##

And the SMTP test:

220 CO9EHSMHS009.bigfish.com ESMTP Service ready
ehlo cci-training.com
250-Requested mail action okay, completed
250-SIZE 10000000
250 OK
mail from:<cwoods@cci-training.com>250 Requested mail action okay, completed
rcpt to:<jerry.willis@workforcesolutions.net>550 Requested action not taken: mailbox unavailable
Who is Participating?
Simon Butler (Sembee)Connect With a Mentor ConsultantCommented:
"bigfish.com" is Microsoft's hosted email scanning service. They are rejecting you for some reason - DNS configured incorrectly, something like that.
ggaither71Author Commented:
I found that after changing providers, we had neglected to configure a 1-to-1 NAT in our firewall.  So all mail was being sent out with the provider gateway IP instead of the public IP of the Exchange server.  Thus no PTR and it had gotten our gateway IP blacklisted in a few places.  Added that NAT and voila.
ggaither71Author Commented:
Set me in motion for checking the IP and PTR information more closely.
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