I have three feature suggestions for the Subscribe by Mail plugin:
1) In the backend, I would like to see more filters added, so the user can choose between confirmed and unconfirmed emails adresses. That will make it much easier to administrate :slight_smile:
2) I would like to see some kind of captcha feature added to the plugin to avoid spam subscriptions. You could try to add a honeypot feature or hidden field to accomplish this.
3) I would like to see an error message added to the subscribe form, so that if a user tries to add an email address which has also been already added they will get an error or message saying "The email address is already subscribed" or something alike.