Reply All from Shared Mailbox removes Sender Address and Duplicates Shared Mailbox Address

[Jacques van der Hoven]

Our scenario is as follows: 

Our client is on Exchange Online and using Outlook 2013. We have 2 people accessing a shared mailbox called Info@mycompany.com
PersonA and PersonB have access to the shared mailbox with full permissions. PersonA and PersonB are able to successfully send and receive from info@mycompany.com

Test Scenario
Send mail from PersonA@mycompany.com TO info@mycompany.com, random@random.com

Test Result

info@mycompany.com and random@random.com receive the email - no problem yet

Test Scenario
PersonA views the email in the Info shared mailbox and hits Reply All

Test Result
Problem exists here where: 
     From = Info@mycompany.com
     To = Info@mycompany.com, random@random.com
Expected behavior: 
     From = info@mycompany.com
     To = PersonA@mycompany.com, random@randomcom

Why would Outlook incorrectly remove PersonA@mycompany.com and incorrectly add info@mycompany.com to the TO field (unecessary since you're replying from info@mycompany.com, the shared mailbox)? 

How do I configure Outlook to fix this? 

[#2]

Most likely becaus Outlook "sees" you as PersonA. So how exactly are you accessing the shared mailbox? This is the expecte behavior when you have the shared mailbox added as additional mailbox (via File -> Account settings -> More -> Advanced), as you are acting as the delegate. If you want the "correct" behavior, add it as additional account instead (File -> Add account -> enter shared mailbox address -> enter *your* username and password when prompted for credentials).

[#3]

We're giving PersonA full permissions on that Shared Mailbox, which in Outlook means we don't add the mailbox at all, Outlook does it by itself. 

[#4]

So Automapping, got it. This is equivalent to the "additional mailbox" scenario, thus the behavior you are seeing. If you want the "correct" behavior, you need to add it as additional account instead.

[#5]

From what you're saying it sounds like Automapping is optional? How do I switch it off and try what you're suggesting? 

[#6]

It's optional, but need to be configured via PowerShell. Remove the permissions and re-add them with Automapping turned off:

Remove-MailboxPermission mailbox -User delegate -AccessRights FullAccess

Add-MailboxPermission mailbox -User delegate -AccessRights FullAccess -Automapping $false

The mailbox will not automatically appear in Outlook then. To add it (as additional account), use the File menu -> Add Account -> Enter the shared mailbox email address and dont enter password. When prompted for credentials, enter the UPN/password of the delegate user.

[#7]

Would doing this have any impact on our ability to convert the shared mailbox to a regular mailbox at a later date? 

[#8]

No, that's simply "client access" method, doesnt affect any of the mailbox properties.

[#9]

Try to use TuneReplyAll tool