Exchange Internet Mail Service

We use EcoTools for Monitoring & Reporting s/w & h/w Counters from our Servers.

EcoTools has been reporting since few days the size of our Exchange (5.5) Internet Mail Service to be increasing continously.
This size has exceeded more than 1.2 GB now.
We are concerned as to how/where in Exchange to look for this & bring down the ever increasing size of this service.