I recently read an article by Dela Quist of Alchemy Worx in the UK DMA Newsletter about the evolving definition of the soft bounce. In the past, email marketers have treated the soft bounce as something of a minor issue, not developing specific strategies for dealing with it. However, as ISPs develop more sophisticated methods for filtering spam, a soft bounce is more likely indicate a serious problem with reputation than just a fluke busy email server.
It used to be that soft bounces were the result of a problem with an individual user’s inbox. A soft bounce was an indication that either the server was busy, the mailbox was full, or the subscriber was on vacation. Because inbox storage limits for most ESPs are rarely an issue currently, it’s highly unlikely that a soft bounce is the result of a full mailbox.
Hard bounces are easy; they result in unsubscribes and subsequent list removal. The marketing standard for a soft bounce is currently to unsubscribe an address if it soft bounces anywhere from three to ten times, which doesn’t exactly indicate much of a sense of urgency. This could pose a problem if your soft bounces are the result of ISP temporary blocking, which they most likely are. Possible causes for ISP temporary blocks listed in Quist’s article include:
1. Poor or unproven IP address reputation
2. Lack of authentication
3. Fluctuations in sending volume
4. Spam complaints for your IP address
5. Sharing IPs with other companies
Clearly, the soft bounce, is maybe, not so soft as we originally thought. Marketers should take soft bounces as signs of clear and present danger to their sending reputation. Investigating soft bounces and determining their underlying causes in a timely manner could prevent major deliverability problems and strenthen your future relationships with ISPs.
