Mail Enabled Public Folder Issues after migration online

Question

Hi
We have recently migrated our Legacy (Exchange 2010) Public Folder Infrastructure to Exchange Online - we have a hybrid setup, SSO and DirSync.
We initially had an issue where some of our mail enabled public folders had lost their link with the associated MailPublicFolder objects and as such could not receive email. 
We resolved this issue ourselves however we are now experiencing a different issue which i believe should be easily resolvable however this isn't the case at the minute.
The issue is that when a user emails a Mail Enabled Public folder Exchange online is attempting to relay the email back to our onPrem servers.  This is occuring for the bulk of our Mail Enabled Public Folders - we have ~1200 of these.  The only
folders that are working as expected are those that had the initial issue above and for which we had to remove and re mail enable these folders.  We also had to recreate any secondary smtp address for these folders.  This accounts for 88 of our total
MEPFs.
I have checked the attributes on the MailPublicFolder objects for those that are not working and those that are functioning as expected.  The only difference in these that I can see is that the MEPFs with the issue have a value set in the ExternalEmailAddressAttribute.
I have tried to programatically set this value to $Null however i receive the following error:
The external e-mail address $null is not an SMTP e-mail address.
I have also tried the following : set-mailpublicfolder -Identity "MEPF"-ExternalEmailAddress "<not set>"
with the same resultAttempting to use the following syntax -externalemailaddress @{remove=$oldAddress} returns the following error:
Cannot process argument transformation on parameter 'ExternalEmailAddress'.Cannot convert the "System.Collections.Hashtable" value of type"System.Collections.Hashtable" to type "Microsoft.Exchange.Data.ProxyAddress".
At present the only fix that I have for this is to take a copy of the email addresses for an affected public folder, Mail disable it, wait for the object to be cleared, re-enable the public folder as a mail public folder and then re-add the email addresses. 
This is ok on an adhoc basis but not for the ~1200 folders that are affected.  Especially when from what i can see it should be relatively straightforward to resolve this with a simple PowerShell script.
I do have a case open with MS for this but I am hoping that somebody here can help also.
Thanks
Joe

Answer 1

Ok so i fixed it myself.
The thinking here is that the ExternalEmailAddress was set using the Primary SMTP address while the Public Folders were on premises.
In order to get the required information we ran a script to export all the MailPublicFolder objects which had a value in the ExternalEmailAddress attribute.  We exported the Name, ExternalEmailAddress and GUID
We then ran a second script to export the Identity, MailRecipientGuid from Get-PublicFolder -recurse. 
The MailRecipientGUID is what ties the Mail Enabled Public folder to the MailPublicFolder object.
Using Excel I then matched the two up and created a csv file with the Identity Attribute from the get-PublicFolder command and the ExternalEmailAddress Attribute from Get-MailPublicFolder.
The following script then used this csv file to first Mail Disable the Public Folder, then Mail Enable the Public Folder.
Once these steps have been completed the final stage is to add the SMTP address back in to the Public folder.
To do this it is necessary to retrieve the new MailRecipientGUID and use it to return the MailPublicFolder for the Set-MailPublicFolder command.
I was happy to use this script after i tested with a small subset of the data.  It is provided as is with no guarantee that it will be suitable for you to use and any use of this script is at your own risk.
Script to Automatically fix brokenn Public Folder Objects
Created By: Joe McGrath
Created On: 18/02/2014
$Path = "C:\PublicFolders.csv"
import-csv -Path $Path | ForEach-Object `
    Disable-MailPublicFolder -identity $_.Identity -Confirm:$False
Write-Host "Broken Public Folders Now Mail Disabled"
Write-Host "Waiting for commands to be fully processed online - the script will continue in 5 minutes"
Start-Sleep 300
Write-Host "Re MailEnabling Public Folders"
import-csv -Path $Path | ForEach-Object `
    Enable-MailPublicFolder -identity $_.Identity
Write-host "Broken Public Folders now enabled"
Write-Host "Now waiting to allow online service to catch up - script will continute in 5 minutes"
Start-Sleep 300
Write-Host "Updating email addresses for broken public folders"
import-csv -Path $Path | ForEach-Object `
    $NewPF = get-publicfolder -identity $_.Identity
    Write-Host $NewPF.Identity
    Write-host $newPF.MailRecipientGuid
    $EmailAddresses = $_.AdditionalEMailAddresses
    $NewMailPF = get-MailPublicFolder -resultsize unlimited | Where-Object {$_.Guid -eq $NewPF.MailRecipientGuid}
    Set-MailPublicFolder -identity $NewMailPF.identity -EmailAddressPolicyEnabled:$FALSE
    Set-MailPublicFolder -identity $NewMailPF.identity -EmailAddresses $EmailAddresses -EmailAddressPolicyEnabled:$FALSE
    Set-MailPublicFolder -identity $NewMailPF.identity -EmailAddressPolicyEnabled:$TRUE
    $EmailAddresses = ""
Write-Host "Completed!"