[ZIMBRA] Prevent loop on notification messages

Connect as zimbra user

$ su - zimbra

Check value of parameter zimbraAutoSubmittedNullReturnPath

$ zmprov gacf | grep 'zimbraAutoSubmittedNullReturnPath'

It should be FALSE :

zimbraAutoSubmittedNullReturnPath: FALSE

Change it to TRUE

$ zmprov mcf zimbraAutoSubmittedNullReturnPath TRUE

Check it again to make sure of the change