Looking for feedback on pricing model for my email marketing tool

I’m building an email‑sending platform and considering a pay‑as‑you‑go model instead of subscriptions. My reasoning is that many people don’t send emails every month, so charging only for usage feels more fair.

However, several founders have warned me that this model may be a mistake from a business perspective.

If you’ve built or used similar tools, I’d appreciate your thoughts on:

• Whether pay‑as‑you‑go is sustainable

• Whether users prefer it

• Any pitfalls I should be aware of

Happy to share more details if helpful.