There's only 1 law in the USA controlling unsolicited e-mail messages: CAN-SPAM Act of 2003. It doesn't differentiate between recipients: as long as a marketing messaging is unsolicited (i.e. there hasn't been a business relationship between the entities) it's in violation of the law. In addition, all marketing messages sent with a preexisting business relationship should comply with the law's technical requirements (message headers, relays, unsubscribe options, etc).
You may not get into legal hot water with unsolicited email ads but you're risking creating a bad name for your company in the industry. It's more effective to develop relationships with potential customers on the basis of feedback of your product than "spray & pray". Cold calls asking for help aren't rejected as badly as cold calls with sales pitches.