Symptoms
61012 Exception from message source [email]: Microsoft.Exchange.WebServices.Data.AutodiscoverLocalException: The Autodiscover service couldn't be located.
Diagnoses
The ConnectionStringEditor.exe shows an Exchange connection string which only had Autodiscover set to true while the rest are left blank. K2HostServer.exe.config also shows that the mail protocol in use is SMTP.
Resolution
Deleted the Exchange connection string.