Troubleshooting email soft bounces

Email soft bounces can have a negative impact on your deliverability. Discover what they are and how to fix them.



It’s easy to focus on the positive metrics, like conversion rate and click-through, to elevate your email campaigns. But what about the negative metrics that are just as important?

For instance, email bounces and email bounce rates are important metrics for the performance of your digital marketing campaigns. After all, your email bounces are a sign of poor sending practice.

In this article, we’ll go over the two types of email bounces and then discuss some tips to troubleshoot common reasons for soft bounces.

What are email bounces?

Email bounces occur when an email service provider (ESP) can’t deliver an email to your subscriber’s mailbox.

Normally, an auto-reply to your message will notify you that your email didn’t deliver and give you a reason for the non-delivery. There are two types of bounces: hard bounces and soft bounces.

Check out the table below for a quick comparison of common reasons behind hard and soft bounces. We’ll get into more detail about hard and soft bounces in the next two sections.

Hard­ boun­ce

Soft­ boun­ce

Hard­ boun­ce

You’­ve trie­d to send­ mail­ to an inva­lid emai­l addr­ess, like­ one with­ typo­s or impr­oper synt­ax.

Your­ reci­pient’s inbo­x is full­.

Soft­ boun­ce

You’­ve trie­d to send­ mail­ to an emai­l addr­ess that­ does­n’t exis­t.

Your­ reci­pient’s emai­l serv­er is offl­ine.

Your­ send­er repu­tation isn’­t good­ enou­gh for the mail­box prov­ider’s stan­dard.

What is a hard bounce?

A hard email bounce means that your email message can’t be delivered because of an unchanging, permanent reason.

This means that there is nothing you can do to fix it. Some reasons behind hard bounces are:

  • The email address doesn’t exist.

  • The email address’s domain name is invalid.

  • Your recipient’s mail server doesn’t exist.

Email delivery isn’t possible in these examples because there isn’t anything to deliver to in the first place. The only thing you can do to avoid hard bounces is validating and verifying your email list. Our Email Verifications API can help you with that.

What is a soft bounce?

A soft email bounce is a type of temporary failure, and as the name suggests, means that your message cannot be delivered due to a temporary reason. Pretty vague, right?

The good news is that this means you might be able to fix the issue and help your email land in the inbox.

Some common reasons for soft bounces are:

  • You’ve had too many hard bounces.

  • You’ve had too many spam complaints.

  • Your server is blocklisted.

  • You have low user engagement.

  • Your recipient’s inbox is full.

  • You send too many messages.

  • The receiving internet service provider (ISP) is having connectivity problems.

So what does an ESP do about it? Here at Mailgun, we’ll attempt delivery a few more times after it bounces. But to keep your sender reputation intact, we’ll stop after several delivery attempts. 

There isn’t a one size fits all solution for soft bounces, but let’s go over the common reasons mentioned above and explore ways in which you can troubleshoot your soft bounces.

How can I troubleshoot my soft bounces?

You need to look at the root cause of the soft bounce to increase your email deliverability and protect your sender reputation, so here are some common reasons for soft bounces and how to troubleshoot them.

You’ve had too many hard bounces

Okay, so above, we said that you couldn’t really do anything about hard bounces, which is true. But you can do your best to prevent them by validating your subscribers’ emails and maintaining your mailing list hygiene.

This is important because if you have a high bounce rate, you’ll send a red flag to ISPs that you’re sending to a poor mailing list and might be spammy. Prune that mailing list to deliver relevant content to subscribers who want your messages to avoid this.

You’ll also want to protect your sign-up forms to prevent some of these non-existent email address from making it into your email list in the first place. Email verification tools like Mailgun’s enable you to validate addresses during the sign up process.

You’ve had too many spam complaints

Not all subscribers want your messages. If they don’t remember signing up for your list or if they can’t find an unsubscribe button, they may mark your message as spam.

Spam complaints send a red flag to service providers. Some ISPs, like Yahoo, state in their bounce message that your email is temporarily deferred due to user complaints.

Reduce spam complaints and avoid the spam filter by using a double opt-in subscription option. This ensures your subscribers know they’re signing up for your mailing list. In addition, offer a clear way to unsubscribe by ensuring all your emails include an easy-to-find unsubscribe link. This way, your email recipients won’t mark your messages as “spam.”

Your server is blocklisted

Your IP reputation and domain reputation are important factors determining your email’s deliverability. ISPs may blocklist your IP or domain based on your sender reputation. This means they won’t deliver messages sent from your IP address or domain.

After identifying and addressing the root issues for the blocklisting, you can either request a de-listing or wait for automatic removal.

You have low user engagement

Some ISPs interpret low user engagement to mean that your emails don’t contain high-quality content. This, in turn, can result in a soft bounce. Employ strategic engagement by targeting specific audiences and use list segmentation to be more relevant to your subscribers.

And, as always, It’s good practice to occasionally prune your mailing lists to remove disengaged users.

Your recipient’s inbox is full

One of the most common soft bounce reasons is that your recipient’s inbox is full. This usually means your recipient provided an email address they frequently use for unwanted marketing promotions.

You can fix this issue by cleaning up your mailing list, employing segmentation, and ensuring your users double opt in to your emails. You’ll also want to ensure your emails provide value to the reader – this way, they won’t want to miss your messages in their inbox.

You send too many messages

We know sending too many emails to senders that have previously opted in is not really spamming, but…let’s be honest, sometimes it does feel a bit like that.

Maintain a consistent volume for your messages, and don’t send emails too often. Some ISPs, like AOL, block or delay non-whitelisted IP addresses when they detect spikes in email sending volumes.

Wrapping up

And that’s it! If you follow sending best practices and keep your mailing list clean, soft bounces shouldn’t plague your email efforts. If you need a little bit more help getting your sending up to speed, let us know and we can find a solution that best fits your needs.

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