Mailchimp Block – Notify if Already Subscribed

### Impacted plugin

Jetpack

### What

Mailchimp Block – Notify if Already Subscribed

### How

Currently, the Mailchimp block shows a success message even if the email was already subscribed.

This can be misleading when a discount coupon is offered (only) to new subscribers (with automation).

The user might not remember being already subscribed, and seeing the success message might wait for the email with the coupon - which will never arrive.

Is it possible to have a "You are already subscribed" alert?

The issue names no files, tests, or entry points, so first locate the Jetpack Mailchimp Block implementation and its existing success-message handling. Reproduce the already-subscribed case, determine how that response is exposed, and add coverage showing that the completed behavior distinguishes it from a new subscription.

Written by the indexing model from the issue text.