conversation history in oulook 2016

Conversation History Add-in for Microsoft Office 2013 is saving the conversation history via MAPI. By default, Lync 2013/ Skype for Business saves the conversations though EWS. Lync/Sfb uses Windows credential manager to authenticate in EWS request. If Windows credential manager provides shared mailbox's credential, Exchange provides access to shared mailbox.
Only when then EWS is not available or there are problems using it, then Lync uses the MAPI protocol through this add-in to connect to Exchange Server and save the conversation history.

There are basically 3 methods to gain access to mailbox:

1. Adding an extra account (only one can be primary)

2. Add mailbox via advanced more 

3. File other users folder (mostly for send receive permissions)

I believe you are doing option one where this issue might occur. 

Can you confirm

Ivan