Summary
Soft bounces are a common occurrence in email marketing, signaling a temporary delivery issue rather than a permanent one. Unlike hard bounces, which indicate an invalid or non-existent email address, soft bounces suggest a recoverable problem, such as a full inbox, a temporary server outage, or an overly large message. Understanding the specific reasons behind these bounces is crucial for maintaining sender reputation and ensuring strong email deliverability.
Key findings
- Temporary Issues: Soft bounces are typically caused by temporary problems at the recipient's end, such as a full mailbox, an inactive email server, or the message exceeding size limits.
- Distinction from Hard Bounces: It's vital to differentiate soft bounces from hard bounces; hard bounces denote permanent delivery failures and require immediate removal of the email address from your list, whereas soft bounces may resolve on their own, as discussed in our guide on the difference between hard and soft email bounces.
- Sender Reputation Impact: While temporary, a high volume of soft bounces can negatively affect your sender reputation, potentially leading to future emails being sent to spam folders or being blocked entirely.
- Greylisting: Some soft bounces can be attributed to greylisting, a spam prevention technique where mail servers temporarily reject emails from unknown senders and require a retry. For more information, read our guide to understanding email greylisting.
- Content and IP Issues: Email content or issues with the sending IP's reputation can also lead to soft bounces, as receiving servers might temporarily defer delivery as a precautionary measure.
Key considerations
- Analyze Bounce Messages: The most effective way to diagnose soft bounce issues is by examining the bounce messages or SMTP error codes returned by the recipient's server. These messages provide specific reasons for the delivery failure.
- Identify ISPs and Volume: Pinpointing which Internet Service Providers (ISPs) are generating the most soft bounces and the percentage of your total sends they represent can help identify patterns or specific ISP-related issues.
- Monitor Engagement and List Hygiene: Assess the age of your email addresses, sending frequency, and typical engagement rates. Poor list hygiene and sending to disengaged recipients can trigger higher soft bounce rates. Regularly cleaning your email list is crucial.
- Content and Volume Adjustments: Review your email content for potential spam triggers and consider adjusting your sending volume, especially if you're sending to new or less engaged segments. You can learn more about this on Mailgun's blog on soft bounces.
- IP and Domain Reputation: Ensure your sending IP and domain maintain a good reputation. Being listed on a blocklist (or blacklist) can lead to temporary rejections, even for valid addresses.
What email marketers say
Email marketers frequently encounter soft bounces and often seek practical advice on how to identify and mitigate them. Their experiences highlight the importance of understanding the temporary nature of these bounces and the diverse factors that can contribute to them, from recipient mailbox issues to sender-side reputation concerns. The consensus among marketers points to the critical need for detailed bounce data analysis to pinpoint the underlying causes and implement effective solutions.
Key opinions
- Diagnostic Starting Point: Many marketers emphasize that the initial step in troubleshooting soft bounces is to identify their classification and the specific providers they originate from.
- Bounce Percentage Matters: The volume of soft bounces should always be considered in relation to the total number of emails sent to determine the actual impact and severity of the issue.
- Recipient Server Issues: A common cause for soft bounces is the recipient's server being temporarily down or under maintenance, as highlighted by Mailbluster's insights.
- Engagement and Age of List: Marketers frequently question the age of email addresses and the typical engagement rates, as older or less engaged lists can be prone to higher soft bounce numbers.
- Greylisting as a Factor: In some cases, a high number of soft bounces can be traced back to greylisting, where a single bot might be repeatedly delayed.
Key considerations
- Understand the Bounce Classification: Before taking action, it's essential to classify the soft bounces to understand their specific nature, which can range from full inboxes to server issues.
- Analyze Provider Data: Investigate which email service providers (ISPs) are most affected by soft bounces, as this can indicate specific deliverability challenges with those providers.
- Contextualize Volume: Always consider the soft bounce count as a percentage of your total sends to gauge its actual significance and impact on your campaign's overall performance. Our guide on acceptable email bounce rates provides more context.
- Review Sending Practices: Examine how frequently you send to affected addresses and their acquisition method, particularly for new contacts, as these factors influence bounce rates.
- Implement Monitoring: Proactive monitoring of soft bounces and a systematic approach to identifying root causes are essential for maintaining good sender reputation and inbox placement. Our article on troubleshooting high soft bounce rates provides further guidance.
Marketer view
Email marketer from Email Geeks recommends starting the investigation into soft bounces by determining their specific classification and identifying the email service providers (ISPs) from which they originate.
Marketer view
Email marketer from Mailgun suggests that a common reason for soft bounces is when the recipient's inbox is full, indicating a temporary storage issue rather than an invalid address.
What the experts say
Email deliverability experts consistently highlight that comprehensive analysis of bounce messages is the bedrock of resolving soft bounce issues. They underscore that general speculation is unhelpful; direct examination of the bounce codes and diagnostic messages returned by mail servers is the only reliable way to understand the root cause. Experts also point to common culprits like ISP-specific filtering, IP reputation, and content issues as frequent contributors to temporary delivery failures.
Key opinions
- Bounce Message Analysis: Experts universally agree that accessing and interpreting the actual bounce messages returned by the sending server (ESP) is the sole definitive method for diagnosing soft bounce problems.
- Avoid Speculation: Any troubleshooting without direct access to bounce messages is considered random speculation, underscoring the critical need for precise diagnostic information.
- ISP-Specific Issues: It is often suggested that specific ISPs, such as Yahoo, might temporarily fail mail due to perceived issues with the sender's content or IP address.
- Identify Sending ISP: Knowing which ISP is responsible for generating the soft bounces is a fundamental piece of information for effective troubleshooting.
- Content and Reputation: Poor content or a low sending IP reputation can lead to temporary deferrals from receiving servers, even if the email address is valid. This is often highlighted in resources like SendLayer's insights on bounce types.
Key considerations
- Prioritize Bounce Data: Always prioritize obtaining the full bounce messages from your ESP before attempting any other diagnostic steps. This data contains the specific reasons for delivery failure.
- Understand SMTP Codes: Familiarize yourself with common SMTP codes associated with soft bounces, as these codes provide critical clues about the temporary rejection cause.
- ISP-Specific Troubleshooting: If a particular ISP is consistently causing soft bounces (e.g., Yahoo), investigate their specific sending policies or requirements for better deliverability.
- Monitor Deliverability Metrics: Continuously monitor your deliverability metrics, including bounce rates, to detect anomalies quickly. Tools such as Google Postmaster Tools can provide valuable insights into deliverability and sender reputation issues.
- Reputation Management: Maintain a strong sender reputation by adhering to best practices, ensuring proper email authentication (SPF, DKIM, DMARC), and avoiding practices that could lead to blocklisting. This is crucial for avoiding temporary blocks and ensuring your emails reach their intended recipients.
Expert view
Email expert from Email Geeks asserts that understanding the full, actual bounce messages returned by the sending server (ESP) is the singular, definitive method for accurately diagnosing temporary email delivery failures.
Expert view
Email expert from SpamResource highlights that temporary bounce codes often indicate issues that might resolve themselves but could also signal underlying deliverability problems that need attention, like IP warming or content adjustments.
What the documentation says
Official documentation from various email service providers and industry bodies defines soft bounces as temporary failures to deliver an email. This documentation typically outlines common reasons, such as full mailboxes, server downtime, or message size limits. It also often provides guidance on how these temporary failures are handled internally (e.g., retries) and advises senders on best practices to reduce their occurrence and mitigate their impact on sender reputation and overall deliverability.
Key findings
- Temporary Delivery Failure: Documentation consistently defines soft bounces as temporary email delivery failures, where the email address is valid but cannot be reached at the moment.
- Common Causes: Frequent reasons cited include a recipient's mailbox being full, the email server being temporarily unavailable or offline, or the message exceeding the recipient's size limits.
- Provider Handling: Many email service providers (ESPs) automatically attempt to resend soft bounced emails for a certain period (e.g., 24-72 hours) before classifying them as a permanent failure.
- Impact on Reputation: While temporary, a high rate of soft bounces can still signal issues to receiving mail servers, potentially affecting sender reputation over time.
- Content and IP Filtering: Some temporary rejections can be due to content-based filtering or reputation issues with the sending IP, leading to deferrals rather than outright blocks.
Key considerations
- Monitor Bounce Categories: Regularly review your email sending reports to identify the categories of soft bounces and track their trends over time.
- Segment and Clean Lists: Actively segment your mailing lists and remove persistently soft bouncing addresses after multiple retry failures, to protect your sender reputation. Learn how to tell if soft bounces were eventually delivered.
- Optimize Content: Ensure your email content adheres to best practices to minimize the chances of being flagged by spam filters, even if temporarily. Our article Why Your Emails Are Going to Spam in 2024 provides helpful tips.
- Address ISP-Specific Requirements: Be aware of specific policies or limitations of major ISPs that might contribute to soft bounces, such as volume thresholds or content filters.
- Technical Compliance: Ensure your email authentication records (SPF, DKIM, DMARC) are correctly configured to establish sender trustworthiness and reduce temporary rejections. Read our simple guide to DMARC, SPF, and DKIM.
Technical article
Documentation from Mailchimp states that soft bounces generally indicate a temporary delivery problem, and they handle these differently from hard bounces by attempting to resend the email multiple times.
Technical article
Documentation from Klaviyo Help Center clarifies that a soft bounce is always due to a temporary reason, such as a full recipient inbox or a momentarily down email server, with their system typically retrying delivery for up to 72 hours.
Related resources
15 resources
Related pages
What is the difference between hard and soft email bounces and how should they be managed?
How to troubleshoot high soft bounce rates and poor inbox placement?
What is an acceptable email bounce rate, and how do hard and soft bounces differ?
How to tell if soft bounces were eventually delivered?
How can I reduce soft bounces after a one-day email volume spike?
Understanding email greylisting and how it works
Why Your Emails Are Going to Spam in 2024 and How to Fix It
Boost Email Deliverability Rates: Technical Solutions from Top Performing Senders
How to Run an Email Deliverability Test: A Proven Checklist
A simple guide to DMARC, SPF, and DKIM
