


If issue persist, then take backup of Conversation History folder and then Delete the same. Reboot your machine and Sign-in to Skype for Business and test IM conversation. You can add below Registry key to solve above certificate issue: (Changing registry may affect your computer OS operation so, take backup of registry before adding or removing registry key.) reg add HKLMSoftwarePoliciesMicrosoftOffice15.0Lync v TrustModelData t REGEXPANDSZ d f reg add HKLMSoftwarePoliciesMicrosoftOffice16.0Lync v TrustModelData t REGEXPANDSZ d f 3. In some cases, Skype for Business client didnt trust the autodiscover certificate if the SMTP domain is different from SIP Domain. Option2: Make sure to keep SIP Domain (Skype for Business) and SMTP Domain (Email) and same. Once folder open delete or rename folders starting sip, like.

On affected Machine: Start Run type localappdataMicrosoftOffice15.0Lync localappdataMicrosoftOffice16.0Lync a.

Also - you may want to make sure that latest Outlook from portal is installed as well. Are you installing the one that say Skype 2015 for Office 365. One other thing - when you installed from the Office portal - there are actually 3 different installs. Interesting - I'm kinda fascinated by your problem because I've seen some unexpected things with Skype in the past.
