Can't send mail to some "dotted" .mil/.gov addresses with Exchange 2007 - error "#550 5.1.3 STOREDRV.Submit; invalid recipient address #SMTP#"

The error in title is returned with an NDR for SOME outgoing emails sent through Exchange 2007 to an address with a dot in the username part of the email address. The server doesn't reject the "dotted" addresses all the time. I just sent a test to "" and it made it OK. Send to "" and it bounces about 1 out of a hundred addresses (the issue is with .gov and .mil recipients). To be clear, it's not that 1/100 sending tries will fail - if the server fails to send to an address it rejects that address all the time.
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augwestConnect With a Mentor Director of Information TechnologyCommented:
Do you have any events in your event log?
Anything in application log??

Also is the SBS2008 a Domain Controller?

Any have you tried to run the best practices analyzer in Ek7 to see if it comes up with any issues?

augwestDirector of Information TechnologyCommented:
Can you post the bounced message?
augwestDirector of Information TechnologyCommented:
Do you have GFI MailSecurity installed on this server
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nvacs_supportAuthor Commented:
From: []
Sent: Wednesday, May 20, 2009 10:28 AM
To: Internal User
Subject: Undeliverable: HIDDEN SUBJECT
Delivery has failed to these recipients or distribution lists:
The format of the recipient's e-mail address isn't valid. A valid address looks like this: Microsoft Exchange will not try to redeliver this message for you. Please check the e-mail address and try sending the message again, or provide the following diagnostic text to your system administrator.

Sent by Microsoft Exchange Server 2007

nvacs_supportAuthor Commented:
No GFI and currently no Exchange-integrated AV. This is running on an SBS 2008, but I hear this happened to non-SBS. Additional note - the public domain for the organization is, but again, I've heard this happened to another EX2007 that was sending from a .com
nvacs_supportAuthor Commented:
Logs looked just like the NDR with no other info. Another user is able to successfully send to the same failed recipient. The user has tried the following:
1. delete the failing recipient from Contacts
2. delete from auto-complete (stored in the "nickname file" outlookprofilename.NK2)
3. manually type every letter of the recipient address
So far no NDR.
Points for being the only responder. Thanks!
nvacs_supportAuthor Commented:
Delete Contact, Delete Autocomplete, Manually Type Address
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