Permission
There is a difference between proactively ‘pushing’ information towards an audience through digital media, and that audience using digital media to ‘pull’ out information that they have made a decision to obtain for themselves.
In the ‘push’ scenario, prior permission must be obtained in the case of any promotional information. This permission needs to be formally documented.
In addition, those who have given such permission must be given the opportunity to withdraw it at any time (e.g. there should be an ‘unsubscribe option’ on promotional emails)

Consider this example

A health professional in the UK complained about two emails sent to him by Galderma, who marketed the botulinum toxin product Azzalure. The first email was an invitation to a symposium that referred to ‘Advanced anatomy to relax, fill and care’. The second email stated that the festive season was a busy time of year for aesthetic clinics and that it was not too late to take advantage of special offers with regard to the purchase of Galderma’s dermal fillers. The complainant alleged that the unsubscribe link on the emails did not work.
Upon investigation, the Panel decided that the symposium invitation was in fact promotional as it made claims regarding Azzalure. Galderma was unable to provide any evidence that recipients of the email would be aware that they would be sent promotional material. They were therefore ruled in breach of the UK Code.