Mailbox is not converted to Remote Mailbox after a remote move

I had an issue recently where a users mailbox was not converted to a Remote User Mailbox after a remote move to Exchange Online. The users mailbox was showing in both Exchange on premises and Exchange Online as a User Mailbox. Obviously this caused a problem for a couple of things:

  1. Mail flow, any users left on premises email the user will have sent to the On Premises mailbox and any users in Exchange Online will be sending to the Cloud mailbox. External messages to the mailbox will be coming in to where ever the external mail delivery is pointed to.
  2. Autodiscover, if the user is on prem then outlook will configure using the SCP and locate the mailbox on premises, and depending on how the public autodiscvoer record is set will determine where Outlook/ActiveSync etc… will point to.

So, the view in the Exchange Admin Centre in 365 shows:

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Yet, the On Premises Exchange Management console shows:

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The problem seemed to stem form a permissions issue for the account migrating the mailboxes and not updating the following AD Attributes:

  • homeMDB
  • homeMTA
  • msExchHomeServerName
  • msExchVersion
  • msExchRecepientDisplayType
  • msExchRecipientTypeDetails
  • msExchRemoteRecipientType
  • targettAddress

So the, the first 3 attributes (homeMDB, homeMTA and msExchHomeServerName) need to be cleared and the other 5 attributes need to be set to the following:


Attribute Value
msExchVersion 44220983382016
msExchRecepientDisplayType 214748364
msExchRecipientTypeDetails 2147483648
msExchRemoteRecipientType 4


The easist way to do this if it is a few users is to run a script manually. If there are a lot of users then you may want to look at using a CSV file for this:

$ADUser = read-host "What is the username of the user affected?"
$TargetAddress = "SMTP:" + $ADUser + ""
Set-ADUser –id $ADUser -Clear homeMDB, homeMTA, msExchHomeServerName -Replace @{msExchVersion="44220983382016";msExchRecipientDisplayType="-2147483642";msExchRecipientTypeDetails="2147483648";msExchRemoteRecipientType="4";targetAddress=$TargetAddress}


When you run this script it will prompt you for the user name of the user and then do the rest for you.

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Once run refresh the Mail Contact view in the Exchange Management Shell and you should then see the account showing as a Remote User Mailbox

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