Had an issue today where i couldn’t send an IM to a federated contact from OWA on Exchange Online and Onprem 2013.
If a federated contact sent me an IM i received the IM in OWA, clicked accept and i could send and receive IMs successfully.
If i initiated the conversion to the federated contact in OWA the IM was not being sent or was flagging up an error.
After some investigation this kb came to light and confirmed this is a known issue and was due to exchange not being able to send the IM correctly due to the address format. boo exchange.
The workaround suggested adding contacts and appending sip: in front of their IM address for example
Also please note sip: must NOT be in capitals as they will fail as well.
I added a contact in OWA and added the IM address with sip: as below
I tested and IM to federated contacts works 🙂
The other workaround from the KB mentions but as i dont use OWA often and was only for myself i just added the OWA contact. For mass groups of user the below would be better.
Create a Contact object in the Exchange Admin Center, and then add the external contact’s IM address to the Proxy Address field. Make sure that the IM address contains the sip: prefix for the IM address of the external contact.