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.