I run a small hobby message board that is entirely non-commercial. People need to provide an email address to register and use that for logging in.
I do not use their email address for anything else (unless they set their profile so that they receive notifications on topic replies or private messages, or if they want to reset their password), and I describe this clearly before registration. Email addresses are never transferred to any third parties, nor are they used for sending any unsolicited messages.
Is this considered a "lawful basis for processing data"? Or is consent required?
It would be important to not require additional consent as I would like the forum to be friendly for teenagers as well, and asking them to print a form and get it signed by their parents is just plain ridiculous and it would turn most of them away (or just cause them to lie about their age instead).