Free electronic mail in exchange for an advert on every message you open – that’s the promise of two Californian start-up companies, Freemark Communications Inc and Juno Online Services LP, both of which promise to have their own advertiser-sponsored systems by the end of the year. Juno’s president, Charles Ardai, figures the average on-line customer spends a minimum of $10.00 to $15.00 a month doing little more than reading mail. Ardai, and his counterparts at Freemark, believe they’ve found a better way: give away the software and on-line time in exchange for exposing consumers to ads. The two firms are counting on customers putting up with adverts in return for a free electronic mail account. Only electronic mail is on offer. Both companies are still comp leting their respective software tests and have yet to line up advertisers and distribution. Although different in origin and execution, Juno and Freemark’s electronic mail services will both include off-line mailer readers – programs that log onto the network long enough to send and receive mail. Users then sort, read and compose mail without being connected and charged for the call. Both systems are Windows-based (Freemark promises to have a Macintosh version next year) requiring upwards of an 80386 computer and a modem capable of 2,400 baud or higher. Freemark is said to be a couple of months away from announcing several key partnerships that it hopes will secure an entry into the US market of computer users who do not have an on-line account yet. It expects to have around 100 advertisers by its launch in the autumn. Juno has concentrated more on getting the software right, claiming If you appeal to users, advertisers will come along. The company is underwritten by New York-based parent investment bankers, D E Shaw. Freemark has raised its millions from venture capital. Neither company is disclosing how much they intend to put into the ventures, but say there is an abundance of cash for the marketing push, including circulating millions of free set-up disks.