How Bounces Can Affect Deliverability

Published September 22, 2010 by David Wilson

Following up on an interesting post on SilverPop's blog about email bounces, they are easy to ignore but keeping tabs on the level of bounces and integrating them into your segmentation strategy will improve your deliverability.

ISPs monitor and watch for IP addresses that continually send to bad mailboxes and get blocked due to complaints—and they will adjust your reputation accordingly. It's important to clarify what the difference is between hard and soft bounces. A hard bounce is a permanent email delivery failure. Some reasons for a hard bounce would be sending to a mailbox that doesn’t exist (bad mailbox) or a domain that doesn’t exist (bad domain). A soft bounce is a temporary email delivery failure. Soft bounces can be caused by sending to a mailbox that’s full or having an ISP temporarily block emails being delivered from your IP due to reputation issues.

Maintaining a hard bounce rate of less than 10 percent, as recommended by most major ISPs. The lower the number of hard bounces you receive, the better your reputation with ISPs. This one is relatively easy to manage by moving your hard bounce email subscribers into your suppression list so they don't just stay on your main list. A tip here is to remember if you're moving lists around, make sure you import your suppressions. 

In terms of handling soft bounces, don’t retry sending to “soft bounce” addresses too soon, leave it a week or two before you resend. And don’t retry sending to “soft bounce” addresses too often, if a soft bounce comes back on the same address more than 2 or 3 times considering suppressing the address.

Checking your reports every time you send is obviously key to this strategy.