- Invalid E-Mail Addresses
- Duplicates
- Bounce-backs
I told you about Invalid E-Mail addresses yesterday. Duplicates are simply what they seem: same E-Mail addresses repeating in your list. This is typically the result of gathering your Contacts from multiple sources. Nevertheless, they need to be eliminated from your Mailings lest users accuse you of spamming their inbox.
Bounce-backs are a totally different ball-game. These are addresses in valid E-Mail format, but messages do not get delivered to them for various reasons. Some reasons are that the E-Mail address does not actually exist, the user account is deactivated, the user's mailbox is full etc.
Situations like the E-Mail address not existing are more permanent and are typically called hard-bounces. Those like the user's mailbox being full are more temporary and are typically called soft-bounces. The point is that soft-bounces can be re-tried later for delivery, while hard bounces will seldom be delivered unless there is a manual intervention.
[ I am using the rider typically as there is no standard definition of what constitutes a hard vs soft bounce - some advocate using error codes, some to base it on at what point it happens etc. However, the basis of how permanent it is a reasonable indicator of the distinction.]
Watch out for such invalid addresses in your Contact list. They effectively bring down your list size by that many.