Over the years, it has been a common practice to convert certain temporary bounces into permanent bounces after a series of occurrences. Some ESPs will escalate bounces that occur X number of times in a row, or occur for X number of days without a successful delivery. One of the most commonly affected bounce types for these suppressions is Mailbox Full.

Mailbox full/over quota bounces are considered by many to be a symbol of a dead address. With the nigh-unlimited storage found in most mailboxes these days, no one who actually checks their email should ever have a full mailbox…right?

Not necessarily. In a new blog post on the MessageGears blog, I sat down with Senior Product Owner of Cloud Operations Nick Zeich-Lopez (aka. ‘Mr. Data’). We pored over results from over 20 billion deliveries and found some surprising results.

For starters, the data showed that of those recipients who experienced a Mailbox Full bounce, over 8% engaged with a subsequent email in the next 7 days and over 31% engaged with an email over the course of the next 12 months.

As a sender who’s suppressing Mailbox Full bounces after the first occurrence, you could be losing nearly 1/3 of those recipients for no reason. At the least, it’s worth some analysis of your own data (or your ESP’s) — you’ll likely find some room for improvement in how you’re handling these bounces.

For the details — along with our findings on bounces caused by spam, delivery timeouts, and DNS errors — check out the full post.

– BG