DeliverabilityList management

Thinking of Using an ‘Old’ List? – Part 3: List Cleaning 101 and Hardbounces

Previous posts:
Thinking of Using an ‘Old’ List? – Part 1: The Risks
Thinking of Using an ‘Old’ List? – Part 2: Prepare your Re-Opt in Email

Hi again, in my last post we talked a bit about reviving old lists and dealing with hardbounces, but I never really got into how important they are. Sure, most people know what a hardbounce is, but I don’t think many people know what kind of an impact sending to them can have on your deliverability.

What is an hardbounce

Very simply a hardbounce is a bounce generated when you send an email to an address that does not exist. It may have existed in the past, but not anymore. Just like calling a phone number that’s been disconnected, you usually get a recording saying “This number is no longer in service..” – which is effectively the same thing. The big difference is, the phone company doesn’t block the rest of your outbound phone calls because you dialed too many wrong numbers!

ISPs look very closely at the number of hardbounces a sender generates. Too many from a given network can indicate a potential Directory Harvest Attack and ISPs will put up a block (usually done automatically) to prevent slow downs which may cause further harm to their users. Have you ever sent an email to a friend and wondered why it took so long to get there? Think about it, if an ISP is being bombarded by millions of spammers trying to validate a list of a ‘gagillion’ addresses, it’s going to slow down the legitimate email from getting through and people will inevitably start complaining.

In order to prevent these blocks, it’s very important to keep your list(s) up-to-date. This means sending on a regular basis and removing hardbounces as you go.

Manage and confirm new leads

Cakemail automatically does this for you, but if you haven’t used the list in a while or like we talked about last week, you’re thinking of using an older list, you need to be very careful. As a preventative measure, which we’ve also mentioned several times, you should be confirming any new leads. When somebody signs-up, you should (at the very least) be sending that address a Welcome email. Not only will this prove they have access to the address, but it will get rid of hardbounces right away and prevent you sending a whole bunch at once. It also gives you an excellent opportunity to send them your From address for Whitelisting and thank them for signing up in the first place!

Bye for now,


If you have any questions, Kevin can be reached at: or feel free to use our Help Desk.

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