There needs to be freely given, specific, informed consent. That is why I have an opt-in checkbox for bulk mails during sign-ups, but there is no checkbox for a drip campaign or similar uses. So, as a user, I have not freely given consent, I have not given specific consent to the drip campaign, nor am a properly informed about having my personal data processes by third-party providers (like Zapier/Mailchimp…), which is certainly relevant in regards to GDPR. Google got a $50 million fine a while ago because of this. They did ask for consent, but the kept it too vague.
The distinction between ads and “helpful information” also doesn’t exist this way. If I run a website as a business, then everything I do is a business activity. If I try to keep my users active with drip campaigns, that a business activity. It doesn’t matter if the specific email tried to sell something or not.