Exchange GUID missing when creating remote mailbox in hybrid enviroment

[he_jac]

I'm trying to find the best and easiest way to create new mailboxes in out hybrid environment.

"The way it has been done here is that we have a created a "cloud portal" where we create the users, and this sync to our AD server which sync to Azure AD. When the new user have been synced to Azure AD and license added, the mailbox is created in the O365 cloud. After this we use Powershell to get ExchangeGuid from O365 mailbox, and logon to on-prem server where we run exchangeShell to enable the remote mailbox and set the ExchangeGuid."

I read that the best practice would be to create the new user from the on-prem server ExchangeShell with "New-RemoteMailbox" so the on-prem creates the AD user object, then when synced to azure AD I assign the lisence and the mailbox is created. This works very good and I have made a script that do most of the work for me. 
But the problem I have noticed is that the mailbox on-prem server never gets a ExchangeGUID, and I still have to get this and run the set command. 

Is there a way around this, to get this to come up correct right away? 
It has made me question if there is an "easy" way for this setup in hybrid environments?

[#2]

That's the expected behavior. You can copy the guid from the ExO Mailbox and populate it On-Prem, it's not that hard to automate.

[#3]

@Vasil Michev Thank you for the information. Then I understand that I wouldn't save so much time with creating the user on-prem as a remote mailbox, like I was hoping. :)
Will have to look at a way to automate it when I have the time, we have this issue with at least 20 of our costumers having Hybrid setup, so I would save some time not having to copy and set the Exhange GUID for them for every new user creation. 

[#4]

Hi how I can can copy the guid from the ExO Mailbox can I get more info please ?@Vasil Michev