What is the difference between soft and hard bounces?

Soft bounces occur due to temporary issues like a full mailbox, a temporarily unavailable server, or a message exceeding size limits. Hard bounces are permanent delivery failures, such as an invalid or non-existent email address. While soft bounces may resolve with retries, hard bounces indicate an irreversible problem.

What causes an increase in soft bounces during holiday weeks?

Common reasons include a surge in email volume, recipients' mailboxes being full, temporary server outages, or stricter filtering by ISPs during busy periods like holidays. Out-of-office replies can also be classified as soft bounces by some systems.

Does a high soft bounce rate affect sender reputation?

Yes, high soft bounce rates can negatively impact your sender reputation. ISPs monitor bounce rates as a signal of list quality and sending practices. Persistent high soft bounces may lead to throttling, blocks, or even being added to a blacklist or blocklist, hindering future email delivery.

How can I diagnose the specific reasons for high soft bounces?

You should export your bounce reports and analyze them by receiver domain and specific bounce codes. Tools like Google Postmaster Tools can also provide insights into deliverability issues with Gmail.

What steps can I take to reduce soft bounces in future campaigns?

Regularly clean your email list by removing inactive subscribers, segment your audience for targeted content, and maintain consistent sending practices. Also, ensure your email authentication (SPF, DKIM, DMARC) is correctly configured and monitor your sender reputation closely.

Why did my email campaign have high soft bounces during US Thanksgiving week? - Troubleshooting - Email deliverability - Knowledge base

Sending a major email campaign during a peak holiday like US Thanksgiving week presents unique challenges. When a significant portion of your emails, say over 860,000 out of 4.3 million, result in soft bounces, it's natural to question if this is a normal occurrence for the holiday period or a sign of deeper issues.

While increased email traffic and recipients being out of office (OOO) can contribute to higher soft bounce rates, a bounce rate of over 20% on a regularly mailed list is indeed surprisingly high and warrants a closer look. Let's delve into the specific factors that might explain such an anomaly during the Thanksgiving week and how to diagnose them effectively.

Understanding soft bounces during peak seasons

Soft bounces are temporary delivery failures, indicating that the email couldn't be delivered on the first attempt, but the sending server (your ESP's Mail Transfer Agent or MTA) will typically retry. Common reasons include a recipient's mailbox being full, the server being temporarily unavailable, or the message size exceeding limits. They differ from hard bounces, which are permanent failures, often due to invalid or non-existent email addresses. During holiday weeks, the sheer volume of marketing emails can strain servers and fill inboxes quickly, making soft bounces more prevalent.

Analyzing the specific bounce reasons is crucial. If a majority of your soft bounces are from

Gmail addresses with messages like "554 5.4.7 [internal] exceeded max time without delivery", this particular bounce indicates that your Mail Transfer Agent (MTA) generated the bounce, not Google's servers directly. This usually means your MTA was experiencing persistent deferrals from Gmail, and after multiple retries, it gave up. The underlying reason for the deferrals could be anything from a temporary technical glitch on

Google's end to a reputation-related issue with your sending IP or domain. Another common

Gmail bounce message, "554 recipient out of storage space", directly points to recipients' mailboxes being full, a scenario that is exacerbated during periods of heavy email traffic like Thanksgiving due to an influx of promotional emails. You can learn more about what causes an unusually high percentage of mailbox full email bounces.

The holiday season, especially around Thanksgiving and Black Friday/Cyber Monday, sees a massive surge in email volume. This can overwhelm recipient mail servers, leading to temporary blockages or throttling of incoming mail. Email Service Providers (ESPs) and Inbox Service Providers (ISPs) like

Gmail and Yahoo implement strict filtering to combat spam and protect user experience. During peak times, these filters might become even more sensitive, treating a sudden, large influx of emails from a sender as suspicious, leading to soft bounces or even direct junk folder placement. This phenomenon is highlighted in various industry observations about increased email bounce rates during holidays.

Moreover, many recipients are traveling or taking time off, resulting in more Out-of-Office (OOO) auto-replies. While most modern ESPs differentiate OOO messages from actual bounces, some older systems or specific configurations might classify them as soft bounces. If your ESP's bounce processor doesn't explicitly exclude OOOs from its bounce count, this could contribute to an artificially inflated soft bounce rate, although it's unlikely to account for such a large percentage on its own.

The role of sender reputation and list hygiene

Your sender reputation is a critical factor in deliverability, especially during high-volume periods. ISPs assess your reputation based on various metrics, including bounce rates, spam complaint rates, and engagement. A sudden spike in soft bounces or spam reports can negatively impact this reputation, leading to more aggressive filtering or even blacklisting. If your emails are going to spam after a high bounce rate, it's a clear signal of a reputation problem.

List hygiene plays a pivotal role in maintaining a good sender reputation and minimizing bounces. Even for a monthly newsletter, if your list isn't regularly cleaned or if it contains a significant number of inactive or disengaged subscribers, you might see higher bounce rates. Subscribers who opted in long ago but haven't interacted with your emails, or those who rarely check their inbox, are more prone to having full mailboxes or flagging emails as spam. Consistent sending volume and regular list cleaning help manage ISP expectations and naturally reduce issues over time. You can learn more about how to reduce soft bounces after a volume spike.

If you also observed a spike in spam reports during this period, that's a significant red flag. High spam complaints, coupled with high soft bounces, can severely damage your domain and IP reputation. ISPs interpret these signals as a lack of legitimate engagement or sending to disengaged audiences, which can lead to your emails being blocked or throttled, resulting in more soft bounces and even getting your domain on an email blocklist (or blacklist). These issues can make it harder to deliver emails, potentially causing them to go to spam more frequently.

Positive email reputation

Consistent volume: Maintain a steady sending frequency to establish predictable sending patterns with ISPs.
Engaged list: Regularly remove inactive subscribers who show no signs of engagement.
Low complaints: Strive for minimal spam complaints by sending relevant content to opted-in users.
Proper authentication: Ensure SPF, DKIM, and DMARC are correctly configured.

Analyzing bounce data for insights

To effectively troubleshoot, the first step is always to dig into your bounce reports. Most ESPs provide detailed bounce logs. You should export these bounces and filter them by receiver domain. Grouping the data by domain and sorting by count from highest to lowest can quickly highlight where the majority of issues are occurring. For example, if

Gmail accounts account for the vast majority of soft bounces, that gives you a clear target for further investigation.

Once you've identified the primary domains, examine the specific bounce codes and messages. For

Gmail, a prevalent message was "554 5.4.7 [internal] exceeded max time without delivery", which points to your MTA's timeout after repeated deferrals, suggesting either a temporary technical hiccup or a reputation challenge with

Gmail. Another common soft bounce reason, "550 [internal] The message is an auto-reply/vacation mail", indicates OOO replies. While these are typically not problematic for delivery, their high volume during holidays could mask other issues or simply inflate soft bounce numbers if not properly categorized by your ESP.

Leveraging

Google Postmaster Tools (GPT) is essential for diagnosing deliverability issues with

Gmail. Check your Delivery Errors dashboard for any spikes around the Thanksgiving week. If your IP and domain reputations (also found in

GPT) remained high and consistent during this period, despite the delivery failure uptick, it suggests that the problem might be temporary or related to volume rather than a lasting reputation hit. You can use Google Postmaster Tools to improve your domain reputation.

It's also worth investigating if the increase in email volume pushed some recipients over their storage limit. The holiday surge can indeed push some mailboxes beyond capacity, as people receive many emails and don't always clear them out. This can lead to "mailbox full" bounces, as described in this SMTP Field Manual entry for Google. Lastly, consider any issues with your email content itself, such as truncation in the inbox due to excessively large email sizes. While not a direct cause of bounces, it can negatively impact engagement and potentially trigger spam filters, contributing to reputation issues.

Strategies for improving deliverability

First, engage with your Email Service Provider (ESP). Request the exact deferral messages for the "exceeded max time without delivery" bounces. These messages contain specific error codes and descriptions from the receiving server that can shed light on why

Gmail was deferring your mail. It could be a temporary network issue, a rate limit, or an indication of a more subtle reputation challenge with

Google. Your ESP's deliverability team should be able to provide this granular data.

Second, prioritize list hygiene. Even for a monthly newsletter, if your audience grew significantly before this send, ensure new sign-ups are genuinely engaged. Implement a regular process to identify and remove inactive subscribers. Regularly cleaning your list can significantly reduce soft bounces caused by full mailboxes or abandoned accounts. Consider a re-engagement campaign for older segments to verify their continued interest. Without proper list cleaning, you might see a sudden spike in email bounce rates, especially from Gmail.

Finally, review your email content and design for potential issues. Ensure your emails are not excessively large, which can lead to truncation in clients like

Gmail. Truncated emails can appear incomplete or unprofessional, potentially leading to lower engagement and higher spam complaints over time. Continuously monitor your sender reputation and deliverability metrics, not just during peak seasons, but consistently to quickly identify and address any anomalies. For a deeper dive into deliverability issues, explore this expert guide to improve email deliverability.

Views from the trenches

Best practices

Maintain consistent sending volume to build stable reputation with ISPs, even during holidays.

Regularly clean your email lists to remove inactive or unengaged subscribers.

Segment your audience based on engagement levels and tailor content accordingly.

Monitor all bounce types and underlying codes for detailed deliverability insights.

Common pitfalls

Sending to an old or unengaged list during peak email volume can drastically increase bounces.

Ignoring specific bounce codes from ISPs, especially large providers like Gmail.

Failing to adapt email content or volume strategy for holiday season traffic.

Assuming high soft bounces are normal for holidays without deeper investigation.

Expert tips

Export bounce data, filter by receiver domain, and group by domain to pinpoint major issues.

Always check Google Postmaster Tools for delivery failures and reputation metrics.

Ask your ESP for exact deferral messages from ISPs to understand root causes.

Be aware of how your ESP categorizes auto-reply/vacation mails in bounce reports.

Marketer view

Marketer from Email Geeks says a soft bounce rate of 20% is surprisingly high, even during a holiday week. ESP bounce processors typically don't count Out-of-Office messages, so further investigation is needed.

2023-12-12 - Email Geeks

Marketer view

Marketer from Email Geeks says that sending to a list that hasn't been mailed in a long time, especially during Thanksgiving week, can increase bounces, as recipients may not recall opting in. Regular mailings help maintain list hygiene and manage ISP expectations.

2023-12-12 - Email Geeks

Navigating holiday deliverability

While holidays like US Thanksgiving bring unique email sending challenges, a soft bounce rate of over 20% on a routine newsletter points to underlying issues beyond just seasonal traffic. It's crucial to look past the initial numbers and delve into the specifics of bounce types, domains, and the precise error messages provided by ISPs.

Prioritizing proactive list hygiene, understanding how your ESP classifies bounces, and diligently monitoring your sender reputation through tools like

Google Postmaster Tools are essential steps to navigate high-volume periods successfully and ensure your valuable messages reach their intended recipients.