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Email Bounces with NDR

CompanyA (Client):  client1@companyA.com,  client2@companyA.com
CompanyB (Our company):  dev1@companyB.com,  dev2@companyB.com

Our employee who is working for the client has got a mailbox on our email server:  dev1@companyB.com
He got another mailbox on client's email server:  client1@companyA.com
On our email server,  we added "client1@companyA.com" as a contact,  and setup a server rule to forward all the emails at "dev1@companyB.com" to "client1@companyA.com".  This forwarding works perfectly somebody sends a mail to our company email address,  it is will be forwarded to the client place email address according to the rule.  But anybody from the client place(having email as xxxx@companyA.com) sends email to dev1@companyB.com,  that email is bounced back to sender with NDR with the following info:
Your message did not reach some or all of the intended recipients.
      Subject:  Testing
      Sent:     3/10/2004 4:50 PM
The following recipient(s) could not be reached:
      Lee, Brian on 3/10/2004 4:52 PM
            There was a SMTP communication problem with the recipient's email server.  Please contact your system administrator.
            <EXCHANGE.companyB.COM #5.5.0 smtp;550 Invalid recipient/sender mailing address>

I checked tracking log on our server,  according to the log:  Our server receives the email from xxxx@companyA.com for dev1@companyB.com,  then, when it is trying to forward the mail to client@companyA.com( forwarding rule),  I see a weird thing, that is--
sender is:  xxxx@companyA.com, receiver is:  clientA@companyA.com

I was guessing that sender should be dev1@companyB.com,  since our server already received the email for dev1@companyB.com.  

If anyone could understand my question,  please respond with your ideas.  If you do not understand my long  question,  see my comment,  I gave a short description.

1 Solution
setascatAuthor Commented:
Short Description:

We set a rule on the server to forward email of a mailbox(dev1@companyB.com)to a contact(ex:client1@companyA.com).  If any one with the email like "xyz@companyA.com" send an email to dev1@companyB.com, they get bounced with NDR instead of email being forwarded to client1@companyA.com.
It looks like your *stupid* echange server, after expanding the alias considers an anti-spam relaying denied.

It's normal that the sender is not expanded. After all, it's a recipient expansion you're making, and there's no reason why the sender would get modified.
If it did, the recipient would have no way of knowing who the mail originates from (they would all appear as beeing from himself).

I'm no exchange expert, but you might try to authorize companyA.com to use your exchange as a relay.
This would be weird, but might work.
Jamie McKillopIT ManagerCommented:
Hello setascat,

I believe the problem lies with the way your client's email system is configured, not your's. You client is most likely runing some type of anti-virus/anti-spam software at their gateway.  As a email sent from the client's domain should never originate from outside their email infrastructure, this usually indicates SPAM and they are blocking it.  When someone from your client sends mail the the employee that is working at their site, the sending domain ends up matching the recipient domain and it is rejected. The easiest way to fix this would be to have your client add the address dev1@companyb.com to the mailbox on their server. That way, email will be delivered directly to the mailbox instead of being forwarded between systems. The only other alternative would be to have them exclude this address from their anti-spam policy, which they may not be willing or have the ability to do.

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