If you are having Outlook client connectivity issue with Exchange 2013 or 2016 try this;
Set-outlookprovider expr -certprincipalname: “msstd:mail.domainname.com”
Set-outlookprovider exch -certprincipalname: “msstd:mail.domainname.com”
To see result;
Get-Outlookprovider
Exchange Server 2013&2016