Be sure to send mails to real addresses! Mailvalidator.io provide a service to validate the existence of email addresses.
Mailvalidator.io need to talk with the mail server of the email address we want to verify to be able to determine if the email address exist or not.
There are 3 possible results for a validation: VALID | INVALID | CANNOT_VERIFY
The email address we are verifying is VALID, exist.
The email address we are verifying is INVALID, doesn't exist.
The email address we are verifying cannot be verified. This is a possible case when the mail server doesn't want to collaborate, the Mail Provider block it or someting else.
We try to provide the best accuracy we can, otherwise due the factors listen above we figured out an accuracy of the 88%-90% on a "normal" email list.