Blackberry maker Research In Motion (RIM) has hit back in its new legal battle, and launched Blackberry Enterprise Server Express, a bid to attract small businesses.

The company, which settled a patent suit with NTP for $612.5 million in March, has counter-sued in the new challenge it faces from Visto.

RIM has asked for three of Visto's patents to be invalidated, and said that it will "consider asserting its own patents against Visto" - moves very reminiscent of the early stages of its long-running struggle against NTP.

Visto sued RIM after a court found that a third mobile email player, Seven Networks, had infringed its patent, and ordered Seven to pay $3.6 million damages. Seven is the number two player in mobile email, with around a million users, compared to RIM's 5 million.

Visto shouldn't count its chickens, though, as Seven hopes to reverse the earlier judgement. "We don't expect to pay any money," said Paul Hedman, managing director EMEA of Seven. "We will be shipping a workaround in the next version which will not use the disputed technology."

BlackBerry Enterprise Server Express is a downloadable version of the server, aimed at small businesses, instead of the large companies that have been RIM's main customer base so far. The software can be used for free, as long as the user company only has one Blackberry handset attached to it. Even for one user, it should be an improvement over the Blackberry Internet Server which is administered by third-party operators.

The Small Business Edition will support up to 15 users, if the company buys licences for them, and users can buy a software key that upgrades it to a full Blackberry Enterprise Server.

Despite this move to encourage Blackberry use in small businesses, RIM is still hampered by the limitation to expensive handsets - its Blackberry Connect scheme to put clients on other phones has not been a huge success as yet. "To reach a mass market, mobile email must be available on a broad range of handsets," said Hedman.