When you try to send an email message to another user inside the same environment from a migrated Exchange mailbox, it generates a nondelivery receipt

Although this article may apply to many different implementations of Microsoft Exchange, it is especially applicable in a deployment of the Microsoft Office 365 Dedicated.

When users try to send email messages to other users inside the same environment from a migrated Exchange mailbox, they receive 5.1.1 nondelivery receipts (NDRs).

For example, Dave@adatum.com sends an email message to Kelly@adatum.com but receives a 5.1.1 NDR.

During a migration phase (or because customers have decided not to migrate all users to Microsoft Online Services), mailboxes exist both in the managed environment and in the customer�s environment. To make correct mail flow easier, the appropriate properties have to be set in each environment.

If the user is NON-MIGRATED and is generating 5.1.1 NDRs:

• Verify that they have an appropriate target address in the managed environment. You can verify this by using Exchange Management Console or ADSIedit.

If the user is MIGRATED and non-migrated users are receiving 5.1.1 NDRs:

• Make sure that the user has a secondary mgd proxy address in the managed environment.
• Make sure that the migrated user does not have a target address value in the managed environment. Although this will not cause a 5.1.1 NDR, it could cause mail to loop between the two environments.

If a user is misconfigured in the managed domain, resolve the situation as outlined here. However, note the SR number, and provide the SI number to the messaging SME to escalate to the technical leads in triage. It is very important to fix these issues quickly for customers and to resolve the tickets. However, we also have to make the appropriate teams aware of misconfigurations. These will be further investigated by the leads as appropriate. Make sure that you take detailed notes that indicate exactly which attribute was changed to resolve the issue.