Ask HN: How hunter.io, rocketreach.co and neverbounce.com verify emails?
These services can verify whether certain emails exist. How do they do it? It cant be that theyre sending emails and wait for them to bounce?
* Valid format: First, we verify the format of the email address is correct and looks something like "email@provider.com".
* Gibberish Email Address: We check to ensure the address doesn't look like a random email address. For example, 1e49cs1pb6@company.com * doesn't pass the test.
* Disposable Email Address: We check if the email address has a domain name used for temporary email addresses.
* Webmail Email Addresses: We verify if the email address uses a webmail like Gmail or Yahoo.
* Presence of MX Records: We check if there are MX records on the domain. If there aren't, the email address can't receive emails.
* Presence of SMTP Server: This check is successful if we are able to connect to the SMTP server (indicated in MX records).
* SMTP Check: We test the email address and see if it bounces or not, without sending an email.
* Accept-all Domain: We check if the server has a catch-all policy which accepts all the email addresses.
For the "SMTP check", they will be doing something like this, programatically: https://www.labnol.org/software/verify-email-address/18220/