Members of shared mailboxes or delegates with ‘Send As’ rights to user mailboxes are unable to send emails – PRB0208829 This issues occurs when using an autocomplete entry that already resides in the Outlook Client auto-complete cache.
Non-Delivery Report – The email address you entered couldn’t be found When attempting to send an email to an existing address stored in your email auto-complete selection list, or a new email address typed in manually, a non-delivery report is received stating that 'The email address you entered couldn't be found.
O365: Platform Sync Timings Please note when the below mentioned actions are performed the synchronisation may take some time. Please allow the synchronisation to complete for changes to take effect.
