Send on Behalf not working in specific situation

[Remco_Tiel]

We've a hybrid exchange 2013 and Exchange online environment where all mailboxes are migrated to the cloud. I've set Send-On-Behalf permissions correctly but it doesn't work if you add the profile in Outlook in a specific way.

send-on-behalf works:

In Outlook365 go to File>Account Settings>Account Settings>select your email address>change>more settings>tab advanced> add the mailbox with the send-on-behalf permission

send-on-behalf does not work:

In Outlook365 go to File>Info>Add Account>follow the wizard

Is it not possible to send-on-behalf in the second situation?

We've chozen for the second option because we've a lot of shared mailboxes, if you add them to your profile a seperate ost file is created instead it is added to your own ost file which could cause performance issues on growth.

Regards Remco

[#2]

@Remco_Tiel Hi, you're doing it manually? You really benefit by using PowerShell 

https://docs.microsoft.com/en-us/powershell/module/exchange/add-mailboxpermission?view=exchange-ps with the -AutoMapping switch.

To answer your question https://docs.microsoft.com/en-us/exchange/collaboration/shared-mailboxes/shared-mailboxes?view=exchs...

To control cache of shared mail folders

https://support.microsoft.com/en-us/help/982697/by-default-shared-mail-folders-are-downloaded-in-cac...

[#3]

@ChristianBergstrom

Thnx for your reply. I've tested the automapping, which works, however automapping is adding the shared mailbox to your own profile (pst) instead of creating a seperat pst file.

[#4]

@Remco_Tiel You mean the .ost I assume. You can use the registry setting if applicable.

I found these on the topic

https://www.michev.info/Blog/Post/2025/how-to-add-a-shared-mailbox-as-additional-account-in-outlook-...

https://www.techpros.com.au/office-365-automapping-performance-issues/

[#5 · Accepted solution]

In the second scenario, Outlook is effectively using Send As permissions, so just add those and be done with it 🙂 If you insist on using Send on behalf of, you need to make sure to always select the "send using" dropdown, as detailed in the article linked above.

[#6]

@VasilMichev 

thnx for the your answer. it is what it is so I'm done with it 😉 and will only use send-as.