Is it ethical to email customers about a new website feature?

Hey everyone, I’m a bit new to the e-commerce space and have an ethical question!

I was wondering if it was ethically okay or made sense to send an email to the customers (not opted-in to receive ‘market emails’) who purchased my products, regarding a new feature of my website. The feature is a community board where the customers who purchased my product can make posts to share the crafts or things they’ve made using the product with other users.

This is a completely free service/platform that I’m providing to create a better user experience and for people with a common hobby to exchange ideas. There will also be free giveaways of merchandise for people who make posts as well. Also, this would be a one-off email, as I’m not planning to anymore features of this sort. What do you think?