Note The conversation history feature uses EWS to create and save the folder. If EWS is unavailable, MAPI is used. As long as EWS or MAPI shows Status OK, go on to the following troubleshooting steps.
Make sure that the client options are configured to save the conversation history:
Locate Skype for Business/Lync Client > Options > Personal.
Under Personal Information Manager, make sure that Microsoft Exchange or Microsoft Outlook is selected.
Make sure that the Save IM conversations in my email Conversation History folder check box is selected.
Note If these options are unavailable, they may be restricted by a Group Policy setting or by the client policy that's applied to the Lync user.
Outlook must be running and have the user's Exchange email set as the default account.
If the user has a high folder count in their mailbox, EWS requests may time out. There's a 1000-folder limit for EWS requests. However, the request may time out if the user is close to the threshold, because a high item count may also increase processing time. To determine the number of folders in the user’s mailbox, use remote PowerShell to run the following Exchange command:
If a high number of folders are verified, have the user reduce the number of folders in their mailbox.