Postini has added discovery features to its hosted messaging services, and has revealed three new service plans.

The new Postini Message Discovery service augments its message archiving service to help customers find archived email and instant messages, particularly ones related to litigation.

The new feature is an optional add-on that can be used to manage internal and external requests for messages. It is designed to make it easier for authorised users to quickly find messages relating to an investigation, the company said. These messages can be saved and exported or put on "litigation hold" to ensure the data is preserved.

Postini has also announced new service plans for its message archiving service. The basic service is for customers that need online digital message archiving; the standard service adds control over storage pools and the ability for users to search the archives for messages; and the professional service provides the standard features plus "immutable" storage of message data, officials said. Pricing was not available.

Last month Google announced plans to acquire Postini for $625 million.