I have a new Exchange 2013 server and connectivity works fine from all clients.
The only exception is the autodiscover on smart phones. iPhones and Android phones are all I have tried. Setting the connection up manually works fine.
Used the testconnectivity site, all test passed ok. Can autoconfigure Outlook from external.
Using a UC cert, all virtual directories configured properly.
CNAME, A and SRV records in external DNS.
No connectivity problems otherwise.
What am I missing?