Hard Bounce
When sending newsletters, some users may not be able to receive the newsletter. There are two types of this, Soft Bounce and Hard Bounce. In the case of a Soft Bounce, it is worth trying to resend at a later date, as it is possible that the user's email account was full at the time of sending and therefore unable to receive the mail.
Hard Bounce is more difficult, as there is a risk that the email address is no longer alive, a typo has occurred or the server has blocked the email.
In order to avoid or at least minimise the number of Soft and Hard Bounces, it is important to validate the email address list before sending, so that we can filter out the addresses that are incorrect.