In a hybrid Exchange environment, if you migrate a user mailbox and then they attempt to access the mailbox using the on-prem OWA (Outlook Web App) link, they will be presented with a page that instructs them to click another link to reach their mailbox and offers a button to create a favorite to the new OWA on O365. Can this redirection page be modified to change the wording, add branding or remove the button to add a favorite?
SnapOverflow
Instructions are here:
https://www.allabout365.com/2012/04/enabling-silent-owa-redirection-for-office-365-hybrid/
The author of the above page states that this is an unsupported solution by Microsoft, so take backups before you make any changes!
You could refer to the official document to simplify the Outlook Web App URL for Office 365 Hybrid https://docs.microsoft.com/en-us/exchange/hybrid-deployment/simplify-owa-url