Hi,

Many users, including myself, reported issues with sending emails through Activesync (Exchange, Googlemail,...). In addition Exchange Servers where being hammered by these upgraded iPhones causing performance issues on the servers itself.

Symptoms
Immediately after updating to iOS 4, some users may notice that Exchange ActiveSync Mail, Contacts, or Calendars do not sync, or sync very slowly. In addition, some Exchange Server administrators may notice their servers running slowly.

Apple released a fix to resolve this issue....
http://support.apple.com/kb/TS3398

Basically read the article with your iPhone, download the configuration file and install it. This will increase the EAS timeout from 30 seconds to 240 seconds.

Sincerely,
Tonino Bruno