Another update has been released by Microsoft to grant full access permissions to send email and respond to calendar invitations on the behalf of another person.
This update will soon be available through Outlook for iOS and Android starting mid-February 2020 with completion by mid-April.
You or your admin can assign full access permissions to a mailbox so that other users can access the mailbox or send email messages that appear to come from the mailbox (using Send As or Send on Behalf permissions). With this latest release, Microsoft are extending this functionality from the desktop versions of Outlook to Outlook versions on mobile devices.
This change affects those who have full access permissions to the owner’s inbox and does not apply to groups. Selective folder permissions will be supported at a later date Microsoft have confirmed.