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Unable to send emails to few users on UNIX from exchange server 2013

Recently worked on a case recently where the customer werent able to send emails to few users who are on UNIX. They do not have the mailboxes on Exchange but have them on UNIX

When they send a mail from a mailbox on exchange to a user on UNIX we see that the mailbox goes to undeliverable queue

Below is the error that we see in the queue

Identity: ServerNameUnreachable149902273

Subject: test

Internet Message ID: <DE625683922DEA4082CD2239458E098F0166D0123C@MB1.MsexchangeGuru.Com>

From Address:

Status: Ready

Size (KB): 4

Message Source Name: FromLocal

Source IP:

SCL: -1

Date Received: 12/03/2015 5:47:37 PM

Expiration Time: 12/05/2015 5:47:37 PM

Last Error: The mailbox recipient does not have a mailbox database

Queue ID: MBX1Unreachable

Recipients:;2;0;The mailbox recipient does not have a mailbox database;1;

There are other accounts where the mails get delivered

When we took the LDP of the working and none working

    How to Take LDP

    On the domain controller follow the below steps

  1. Start à Run type LDP and hit enter.
  2. Click on connectà you will get a pop screen please click ok


  3. Again, click on Connection and click on Bind you will get pop up screen, click on OK on that screen as well
  4. Go to View and click on tree, you will get a drop-down screen, Choose your domain container from the drop down
  5. Then look for the OU in which the user, in our example its and
  6. On the right hand, you will have the attributes populated. Post selecting the required User click on Connections and select New, this will clear all the attributes on the right-hand pane
  7. Now double click on the User to get the attributes repopulated, once it’s populated do a right click on the right pane and select all and save it on a notepad.
  8. Repeat the same for the other User.

When I compared the working user and the non-working user we see that the non-working user has proxy address stamped even though he does not have a mailbox on the exchange server. I think the proxy address was stamped because of O365 migration and the customer says that the o365 team was doing some change with the Email address policy.

Instead of removing the Proxy address we added it to the target address so that when we send the mailbox proxy address is ignored and the emails is sent to the target address

Ratish Nair

Microsoft MVP | Exchange Server

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