You have seen that exchange 2010 has introduced the feature called auto-mapping where mailboxes
get auto mapped to outlook when full mailbox permissions are granted.
We have seen issues with this feature & that’s why in the past I have written the post on
how to disable the auto-mapping for all mailboxes in the environment.
https://syscloudpro.com/2015/05/04/disable-auto-mapping-of-exchange-mailboxes/
Things have come a long way since than but some administrators are still not comfortable with this feature.
This feature is also part of Exchange online but needs to be disabled differently than what we have done on On-premise.
Exchange On-premise Uses Autodiscover & also “msExchDelegateListLink” attribute for Automapping , In the above blog post ,
We have fetched all mailboxes in the environment & set the “msExchDelegateListLink” attribute to null where applicable via Powershell script.
This can also be accomplished by using below powershell command as well by removing the permissions first & than adding the permissions
by setting -automapping parameter as false.
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Add-MailboxPermission -Identity Mailboxname -User Username -AccessRight FullAccess -Automapping $false
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In Exchange online environment where you are maintaining Hybrid , attribute msExchDelegateListLink doesn’t gets updated.
So how you can mass disable this without removing/re-adding permissions ??????????????????
This is possible as Microsoft has provided a good powershell way to accomplish it 
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Remove-MailboxPermission mailboxname -ClearAutoMapping
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You can fetch all mailboxes & schedule this command to remove it from all users.(you can just
filter it on shared mailboxes as generally those are ones used for mapping)
I will also check if there is other way to do it where we can detect which all mailboxes are using this feature & just act on those ones,
till than stay tuned
Thanks for Reading
Sukhija Vikas
