GudenSoft Email Scheduler is a tiny little utility with huge functionality. It will enable you to customize and change the polling interval your device uses to check for e-mails on your e-mail accounts in the same manner ActiveSync does, but this time on all your accounts in one place.
You can have separate scheduling settings for separate accounts, according to service availability and/or data rates.
After downloading and installing, it will recognize all you currently setup e-mail accounts and will show you the options to choose. In order to run this, your device must have Windows Mobile Professional 5.0 or above featuring .NET Compact Framework 3.5.