ECP 2013 redirects you to OWA 2010 or 2007
If you have a mailbox on an older Exchange server (2007 or 2010) and you are trying to login to Exchange 2013 ECP you may find that you will be redirected to OWA on the old server. To get around this use the following URL:
https://<Exchange_2013_CAS_FQDN>/ecp?ExchClientVer=15