If Egress is stuck sending emails then the below can be used as a temporary fix.


To apply this fix we will have to use PowerShell.


Firstly, connect to exchange with the following:

    Connect-ExchangeOnline



If you get an error connecting then the exchange module will need to be installed:

    Import-Module ExchangeOnlineManagement



Once connected run the below to apply the fix.
    Set-CASMailbox -Identity Insert user email -OwaMailboxPolicy EgressOnSendPolicy