Mail.com, a New York-based e-mail and fax marketing company, said Monday that it surpassed 8.4 million in weekly e-mail advertising impressions delivered through its special delivery service for the quarter ended in March. That's a 40% increase from the same period a year earlier. Across all its services, Mail.com said it delivered 2.1 billion impressions last quarter, a 379% increase from a year earlier. Although the company specializes in business-to-consumer advertising, it sees an untapped b-to-b market ready to grow. Meanwhile, Advertising.com, Baltimore, said its revenue grew to $3.5 million in the month of February, as the new advertising network continued rapid expansion. Sales were up 1,600% in 1999, and the number of employees grew from 10 to 250, Advertising.com said.