I recently had the experience of migrating a client to Office 365. While most things went smooth, one user who was using Outlook 2007 wasn’t able to open one of the shared mailboxes. Every time she tried to open the file, the following error message would appear:

[callout] Cannot expand the folder. The set of folders cannot be opened. Microsoft exchange is not available. Either there are network problems or the exchange computer is down for maintenance.[/callout]

I tried removing her profile and rebuilding it again, but to no avail. I was able to open the inbox using Outlooks option of File > Open & Export > Other Users Folder. I was also able to open the mailbox it in OWA.

In the end, the problem was related to the AutoMapping function of Exchange and Outlook. To solve the problem I had to do the following things:

1. Connect to O365 using your usual Powershell Connection lines:

$LiveCred = Get-Credential
$Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://ps.outlook.com/powershell/ -Credential $LiveCred -Authentication Basic -AllowRedirection
Import-PSSession $Session

2. Remove FullAccess permissions for the affected user from the shared mailbox

Remove-MailboxPermission (SharedMailbox) -User (UserAccount) -AccessRights FullAccess

3. Add Full Access permissions back on, but make sure you set AutoMapping to FALSE!

Add-MailboxPermission (SharedMailbox) -User (UserAccount) -AccessRights FullAccess -AutoMapping $false

4. Use Outlook to add another user’s mailbox by editing the account and adding the user by choosing (in Outlook 2013) File > Account Settings > Change > More Settings > Advanced > Add. The dialogue should look like below. Simply add the user’s in the Add dialogue and you should be good to go!