Recommendations for emailing a past and current customer list

In the past, I used intercom.io to manage all outbound messaging to past and current customers. It worked well but became very expensive after my start-up intro pricing.

I transitioned to Helpscout to manage customer support, which has been doing well (I miss the GitHub integration, though). It's cheaper, but I'm missing an easy way to send outbound emails.

What I'm looking for...

I want a way to send an email to a list that automatically syncs with my Stripe customer database. The email is a plain text email.

I'm currently using Convertkit, but I feel like this platform (and Substack) is more for generating new readers and writing to them, vs. being used for product update emails. It also doesn't sync my customers from Stripe.

What service do you recommend, or would you roll your solution internally?