Outlook 2013 as part of 365 Business Full exchange mail account.
Just recently mail I send to a client who is also using 365 with full exchange is either not being delivered/received at the recipients address. Nothing has been changed at either end, and has all been OK since Oct14
I have sent test mails, including ones without any signature and also set both delivery and read receipts on a test mail.
Client now informs me he received two test msgs, sent today, and has now just received two mails I originally sent on 27/05/2015
I received the delivery receipt but the read receipt returned "contained an option unknown to Outlook, therefore receipt generation failed"
What is bizarre that I use payroll software and send payroll data within that to the client, this is all being received. I'm using the same mail address in the payroll software as when I send from OL2013 itself.
T/Y
David