OPush is an implement of the Exchange ActiveSync protocol supporting versions 2.5 and 12.1 of the protocol (Exchange 2003 and 2007). It is implemented with Eclipse and OSGi technologies and allows customized data providers. A default data provider implementation is available for the OBM groupware solution.
exJello is a JavaMail provider that connects to a Microsoft Exchange server (actually, it uses the WebDAV interface exposed by Outlook Web Access). It is designed as a drop-in replacement for the standard POP3 and SMTP providers. This allows you to send and receive messages through your Exchange server in situations where a POP3/SMTP interface is not available (through a restrictive firewall, for example, or if your administrator simply does not provide a POP3 or SMTP gateway).