I've got a good kind of pricing update today.
To bring our customers costs down, we’ve implemented a feature that checks every email we collect and auto unsubscribes them if we think it’s going to bounce. We do this via two methods: MX record check and email validation against the RFC specs.
By default, MX records are required in DNS. MX or "mail exchanger" records tell where to deliver email for the domain. Many domains run their website on one provider (ISP, Heroku, etc.), and email on a different provider (such as Google Apps, Zoho Mail, etc). If we scan an email, and notice there are no MX records then it's safe to assume that the email won't get delivered so we auto-unsubscribe the visitor on upload and identification.
As an example take example.com. While a valid domain name, it does not have MX records so any email that uses it will be auto-unsubscribed.
Then, after we've confirmed that the email has MX records we'll run it against the RFC specifications to make sure the email is compliant. This sounds like a good idea, until you learn about all the crazy ways people write out there email. For now, we just check against some basic measures and if it passes the visitor remains subscribed.
We plan to improve this over time, but for a first stab at it I'm pretty happy. If you have feedback or a recommendation, just let me know.