For context, the built-in "Send email" actions leverage SendGrid. If you've set up your own SendGrid key and are relying on SendGrid's free plan, you're likely affected by SendGrid's discontinuation of their free plan which they recently announced (read it here).
What SendGrid's Discontinuation of their Free Plan Means For You
Bubble’s built-it email functionally will continue to work as usual
For users that want to use their own key, SendGrid will still have a 60 day free trial (without credit card) of their service but should plan on alternatives if they are looking for a fully free service
Next Steps
There are plenty of other free email service providers that still have free tiers like Postmark, Resend, SMTP2Go, AWS SES. We recommend that users do their own research to find a provider that fits their needs.
To reiterate
Bubble’s out the box functionality won’t change. This affects users that depend on a free-tier plan with SendGrid. Those users should review and plan according to these news.