Hard Bounce

A hard bounce is an email message returned to a sender tagged as permanently undeliverable. For legitimate senders, who use one or more methods of opt-in subscription practices, this is usually caused by a recipient who closes and/or changes their email address.  Other reasons for hard bounces reported can also be caused by typos, or domains that are no longer valid. Hard bounce reports are also a key element for a sender’s reputation score and if a rented or purchased email address list is used then the instances of hard bounces will most likely be a reason for an IP to be blacklisted.  Additionally, it is rare, but a network failure on either the sender or recipient’s end can cause an email to be labeled as a hard bounce.

There are a few steps that can be taken to reduce hard bounces:

Use a service or application that deletes hard bounces to keep subscriber lists clean.

Use a double opt-in subscription method

Track your open and bounce rates by major domain and if one has higher bounce rates than others, then review their spam and block policies and make sure you are adhering to their standards

Test, test, test: There are a few services on the web that will test for you- some free but usually those are less reliable than the pay-for plans.