What it means
Under regulation 22 of the Privacy and Electronic Communications Regulations, you may send marketing email or text to someone whose details you obtained during a sale or negotiations for a sale, about your own similar products or services, provided they were given a simple chance to refuse at the time and in every message since.
Why it matters to a small business
It is the legal basis a small business emailing its own customer list is relying on, often without knowing it, and it is narrower than people assume. It covers your customers, not everybody whose card you were handed. It covers similar things, not everything you sell. And the opportunity to refuse has to have been there when you collected the address, not bolted on afterwards.
The bit people get wrong
It does not cover a list you bought, a business card in a fishbowl, or names scraped from a directory, and it is not a licence to email everybody who ever enquired but never bought. If you cannot say which sale or which negotiation an address came from, you are not on soft opt-in and you need consent.
Source: ICO guide to PECR and direct marketing. This page is a plain-English summary written by the Marketeer team, not legal advice. Where money or the law is involved, read the source.