Understanding and Reducing Soft Bounces

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Getting your email delivered is the first step to successful email deliverability. Once an email is successfully sent, it either gets delivered or bounces back – there is no in-between. It can be a considerable challenge to ensure your email is delivered to the inbox, but when your email bounces, it indicates a bigger problem: the email didn’t even clear the first hurdle in the delivering process.

Hard vs. Soft Bounces

Traditionally, a “hard bounce” indicates a permanent reason an email cannot be delivered. The usual reasons are an invalid email or an invalid domain.

“Soft bounces” have been defined as temporary failures due to an unavailable server, a full mailbox, or an oversize message. While those causes still hold true in theory, they no longer represent the top reasons behind today’s soft bounces, which are mostly caused by ISP blocks. In most cases the blocks are temporary and can often be resolved by identifying the root causes, then following email best practices and ISP guidelines.

Here are six of those reasons, with suggested remedies:

1. A High Hard Bounce Rate Can Trigger Soft Bounces

Having too many invalid recipients – i.e., a high hard bounce rate – is a clear sign to ISPs that you are sending to a poor mailing list and may consequently incur a temporary block. At Act-On we consider a high hard bounce rate to be anything higher than 1%. The most effective way to reduce the number of hard bounces is by cleaning your list regularly of invalid addresses through an email validation service.

2. Too Many Messages Sent

Volume consistency is a vital component in deliverability, and ISPs are always on the alert for any irregular sending activity such as spikes in email volume. AOL, for example, tends to block or delay non-whitelisted IP addresses when they detect such unfavorable statistics. Fortunately, if you have a good reputation with AOL, you can apply to be whitelisted. If not, then it’s time to segment your list and maintain a consistent sending schedule. First segment your list by engaged and unengaged recipients. Then stagger your sends to the unengaged over a time length you specify, for example, four hours. (Act-On can manage this staggered send for you.)

3. Spam Traps Hit

This is another way for ISPs to determine the reputation of a sender – and another reason why list hygiene is so important. Most spam traps can be identified and removed by a data cleaning service. If not, they are usually hidden in your inactive list, as they generally don’t engage with any email. By suppressing the unengaged segment, one of my clients recently was able to resolve a temporary block at Comcast that used to occur every single time they sent to their Comcast recipients.

4. Too Many Spam Complaints

Spam complaints are probably the most negative engagement signal you can ever generate from your email. Some ISPs, such as Yahoo, will clearly state in their bounce message that your email is temporarily deferred due to user complaints.

In general, an acceptable spam complaint rate is below .1% (one per thousand). If you are consistently exceeding the threshold, then you should seriously consider using double opt-in and adding an opt-out link to the pre-header of your email, and/or scaling back frequency for your unengaged recipients to reduce the number of spam complaints.

5. Your Server is Listed on Blacklists

Depending on which filtering products and blacklists your recipient ISPs employ, your email could bounce back if your IP or domain is listed on a blacklist. All of the factors aforementioned can get your server blacklisted but the most common cause is spam, as that’s the key thing the blacklists are designed to stop. Spamhaus, for example, is currently the most influential and authoritative anti-spam blacklist out there. If you are listed on Spamhaus, soft bounces will follow immediately as most (if not all) of the reputable ISPs use this blacklist. Once you have identified and resolved the root issues, you can either request a delisting from the blacklist (some blacklists do not allow delisting requests; others do) or wait for automatic removal. Blacklists monitor your sending activity constantly, so delisting can happen in real time as soon as the blacklist sees positive change.

6. Spam Content

 With more ISPs incorporating user engagement into their algorithms, content nowadays carries less weight in the filtering process. Optonline, for example, tends to reject a portion of your email sends due to “spam content” but at the same time delivers the same “spammy” message to certain recipients, suggesting multiple factors at play. I’ve worked with my clients long enough to know that sending good content to a poor list can be way more detrimental than sending bad content to a good list.

There are certainly more soft bounce types than what I have listed above, but it all comes down to following email deliverability best practices to ensure your email has the best chance of being delivered and reaching the inbox. To learn more about the critical factors that can affect your deliverability, download Act-On’s free ebook – Best Practices in Email Deliverability.