Shared mailbox: Use send-as, not send on behalf from Outlook 2016

Hello,

We have a lot of shared mailboxes. For every shared mailbox, we create a specific security group that contains the members who should have access to that particular shared mailbox.

We give full mailbox permissions and send-as permissions for that particular security group onto the shared mailbox.

For example, security group A has full mailbox access and send-as permissions onto shared mailbox A. By adding users to security group A, they have full access to the shared mailbox.

We create every new shared mailbox/security group combo using Powershell. That has been working flawlessly for the last years.

However, for a recent new shared mailbox/security group combination, when a user that's member of the related security group wants to send an e-mail from the shared mailbox (by changing the from field in Outlook and selecting the shared mailbox from the global address list), Outlook tries to send every time 'send-on behalf'. This only happens for that newly created mailbox.

I compared the output of Get-Mailbox and Get-RecipientPermission for the new problem shared mailbox and an older shared mailbox (which enable users to send mail send-as from outlook just fine) but I couldn't find any differences.

For your information, that's the error we get back immediately after trying to do a send-as for the new shared mailbox:

Your message did not reach some or all of the intended recipients.

Subject: Test from Outlook

Sent: 23/11/2017 9:27

The following recipient(s) cannot be reached:

name of sending user on 23/11/2017 9:27

This message could not be sent. Try sending the message again later, or contact your network administrator. You do not have the permission to send the message on behalf of the specified user. Error is [0x80070005-0x0004dc-0x000524].

Why does Outlook always tries to do a send on behalf (what we don't want) where else for other shared mailboxes, send-as works fine?

Using send-as from OWA however works just fine for the newest shared mailbox. It only seems a problem related to Outlook (tested on multiple clients that have access to the shared mailbox) and that particular new shared mailbox.

Thanks in advance.

VasilMichev
Nov 23, 2017
The behavior depends on how you've added the shared mailbox in Outlook (automapped vs additional account), and of course by the method you use to compose the message. Check my ramblings on the topic here: https://www.michev.info/Blog/Post/1430/

VasilMichev
MVP
Nov 23, 2017
The behavior depends on how you've added the shared mailbox in Outlook (automapped vs additional account), and of course by the method you use to compose the message. Check my ramblings on the topic here: https://www.michev.info/Blog/Post/1430/
- Tom Glorieux
  Copper Contributor
  Nov 24, 2017
  When choosing the From address using the Global Address List instead of the offline one, I'm now able to send-as. :)
  
  Thanks for the help
  - Ron Schmitt
    Copper Contributor
    Aug 07, 2018
    What's odd is that--- - yes when i choose the From, from the ONLINE Global Address list -- it works. However on subsequent emails, the autocompleted address does not. It seems i have to click into the Online GAL on each and every message I send.
    
    Is there any way to avoid this?
- Haneef Ibn Ahmad
  Iron Contributor
  Mar 11, 2018
  Very insightful article! Thanks.
  
  Do you have any piece on the differences between: Shared Mailbox, User mailbox that is shared, Office 365 group, and Mail Enabled Security Group.
  
  Thanks
  - VasilMichev
    MVP
    Mar 13, 2018
    Difference in terms of the Send As functionality, or in general? For Send As, it doesn't matter that much what kind of object you have, as long as you have the necessary permissions. The difference is mainly in how you want to handle the messages (i.e. gather them centrally in some mailbox), as different objects can have different methods to use on that part.
- WMauney
  Copper Contributor
  Jul 15, 2024
  Your link goes to an article titled 'Postpone the deletion of your SharePoint Online Public website'. any chance you have the correct post somewhere?
  - PvanVoorst
    Copper Contributor
    Nov 04, 2024
    WMauney : https://www.michev.info/blog/post/1430
Daniel_Cardoso
Copper Contributor
Feb 01, 2024
Hello,

I solved it with the following solution, in Exchange in the Shared Mailbox, uncheck the "Hide from address books" option, wait about 5 minutes, close and open Outlook to reload the address list or force it to update in the Outlook menu, after that in send how to select From to choose the email directly from the address list (It may sometimes take a while for it to appear, but be calm, remember to remove what you had already saved from the list), after that try again, in my case it worked in time and before I was having the same problem.
OnezoTom
Copper Contributor
Feb 20, 2024
Tom Glorieux I was trying to get this work using various fixes on forums for a good few hours before I managed to get it to work.
As many people have already stated in online forums, when you remove the address from the "From" list in outlook and then reselect it from the "Global Address List" it works fine for one email, but subsequent emails fail to send.
For some reason, the Outlook desktop client must use the "offline global address list" by default even after you change it.
The fix for us was fairly simple in the end:
1. Go to "Send/Receive" tab and select "Send/Receive Groups"
2. Click "Download Address Book"
3. Ensure the choose address book field says "\Offline Global Address List" and click OK.

Once the download has finished, the emails sent as the correct mailbox every single time. I have no real clue as to why this would be the case, but I'm guessing it updates the permission list on the mailboxes for the outlook client?

But it worked!

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Shared mailbox: Use send-as, not send on behalf from Outlook 2016