I know Mandrill has webhooks that can notify you of events such as bounced emails. https://mandrill.zendesk.com/hc/en-us/articles/205583217-Introduction-to-Web

I know Mandrill has webhooks that can notify you of events such as bounced emails. https://mandrill.zendesk.com/hc/en-us/articles/205583217-Introduction-to-Webhooks https://mandrill.zendesk.com/hc/en-us/articles/205583217-Int... Wouldn't integrating this help solve the issue, as you can possibly check if you received a bounce for that email shortly after the user attempts to register, and then notify them on the screen?