I get the following error using outlook 2016:

Your message did not reach some or all of the intended recipients.

 

      Subject:     RE: Birthday

      Sent:  21-Jun-16 16:55

 

The following recipient(s) cannot be reached:

 

      'Exxx xxxxx' on 21-Jun-16 16:55

            553 Relaying disallowed as <xxxx@outlook.com>

Whenever I reply to an email in my zoho inbox, my outlook.com account is automatically chosen as the default reply address. Zoho is set as the primary and default address in outlook 2016, but that does apparently not apply to the reply address.

The email is then completely and not in the "send folder of either account.