MAPISP32.EXE ???

What exactly does MAPISP32.EXE (Microsoft Windows(TM)Messaging Subsystem Spooler) do and ho can I stop it from dialling my internet connection every few minutes?

I connect to an ISP via ISDN and even when there are no web based apps running the connection autodials every few minutes. I have Zone Alarm Firewall installed and it often tell me that Microsoft Windows(TM)Messaging Subsystem Spooler had connected.