Hard Bounce...

A hard bounce is when an email is sent to an invalid or non-existent address. ISP’s are less tolerant with these because lists should all be opt-in, so why would you have an incorrect email address on your list, right? Fact is people change jobs, change their email addresses and last thing on their mind (hate to say) is to update their details with companies that send them regular email campaigns. Of course these hard bounces are also expected from any large list, which is why list hygiene is so important. ISP’s automatically block access when a message is sent to an invalid email address and will continue to block you until it’s removed from the list, so it’s much easier to simply comply and delete the offending email address.