Autodiscover doesn't work on iPhone

Error description:

While configuring an Exchange email account on iPhone, the autodiscover of the Exchange server doesn't work: you have to put in the CAS servername in order to get it working.

Symptoms:

While the test performed by Microsoft Remote Connectivity Analyzer gives a positive result, the autodiscover doesn't work on the iPhone.

Solution:

There are 4 ways of implementing Autodiscover for Exchange 2010:

Set the SCP to the url of the autodiscover server
DNS/HTTP redirection
locally configured XML file
DNS SRV records (most used method for Autodiscovery)

iPhone 3G/4 supports method 2 (DNS/HTTP) but doesn't support the DNS SRV records method.

Typically, the SCP method is used on the internal network. The scp (service connection point) is published in the Active Directory. For clients outside the internal network, the DNS SRV records are used.