Electronic mail marketing
The most important thing to remember is that you can only carry out unsolicited electronic marketing if the person you're targeting has given you their permission.
However, there is an exception to this rule. Known as the 'soft opt-in' it applies if the following conditions are met;
* where you've obtained a person's details in the course of a sale or negotiations for a sale of a product or service;
* where the messages are only marketing similiar products or services; and
* where the person is given a simple opportunity to refuse marketing when their details are collected, and if they don't opt out at this point, are given a simple way to do so in future messages
When you send an electronic marketing message, you must tell the recipient who you are and provide a valid contact address.
The rules on emails don't apply to emails sent to organisations, though you must still identify yourself and provide an address.
The Telephone Preference Service (TPS) and Fax Preference Service (FPS) are operated by the Direct Marketing Association, and allow people to register their numbers to opt out of receiving unsolicted calls or faxes. You must not market individuals or organisations who have registered their numbers with the TPS or FPS.
In summary, we recommend that your marketing campaigns are always permission-based and you explain clearly what a person's details will be used for. Provide a simple way for them to opt out of marketing messages and have a system in place for dealing with complaints.
You'll find a brief overview of the electronic regulations at Privacy and Electronic Communications – your legal obligations but before you start any marketing campaign, we advise you to read our detailed guidance notes.
from here