Which channel of direct marketing requires opt-in consent under GDPR?

The channel of direct marketing that requires opt-in consent under GDPR is business-to-consumer emailing and text messaging. Under the General Data Protection Regulation (GDPR), personal data processing, including marketing communications, must be done transparently and with the permission of the individuals involved.

For email and text message marketing, the GDPR stipulates that businesses must obtain explicit consent from individuals before sending them marketing communications. This is primarily because such channels can be considered invasive, as they reach people directly on their personal devices. The requirement for opt-in consent ensures that individuals have a clear choice and are fully informed about what they are agreeing to.

In contrast, while postal marketing does have some regulations, it does not require explicit opt-in consent under GDPR, as long as the sender respects the individual's right to object. Telemarketing does have specific regulations as well, but again it generally operates under different consent frameworks compared to email and text messaging. Therefore, business-to-consumer emailing and text messaging stands out as the correct answer due to the stringent requirement for opt-in consent for these particular channels.