I think that may depend on the definition of ‘customer’. If you ask for a catalogue by email but don’t buy anything, the company may regard you as a customer. But for them to keep your email address will require your consent, as there is unlikely to be another lawful basis available.
I’ve not long been a subscriber of your blog but, as a DPO, I like your style and your sensible comment. The above message is one I’ve personally laboured over.
informationrightsandwrongs 
I think that may depend on the definition of ‘customer’. If you ask for a catalogue by email but don’t buy anything, the company may regard you as a customer. But for them to keep your email address will require your consent, as there is unlikely to be another lawful basis available.
They might well rely on legitimate interests, but you’ll appreciate I’m trying make a point for effect, not to provide detailed analysis.
I’ve not long been a subscriber of your blog but, as a DPO, I like your style and your sensible comment. The above message is one I’ve personally laboured over.
Thanks!
You have no idea what a fantastic resource this website is. If only you posted every day. Thanks Jon.