Why am I getting soft bounces and how do I fix them?

Summary

Soft bounces are temporary email delivery failures stemming from issues like full mailboxes, server downtime, or graylisting. Analyzing SMTP response codes and ESP bounce messages aids in diagnosis. Addressing these requires ensuring email content relevance, list hygiene, proper authentication (SPF, DKIM, DMARC), monitoring sender reputation, and maintaining consistent sending volumes. ESPs automatically retry delivery, but addressing underlying problems and adhering to provider guidelines is essential to prevent soft bounces from turning into hard bounces.

Key findings

  • Temporary Nature: Soft bounces signify temporary email delivery failures (4xx SMTP codes).
  • Variety of Causes: Common causes include full mailboxes, server downtime, graylisting, and DNS issues.
  • Automatic Retries: ESPs like Amazon SES, Twilio SendGrid, and others automatically retry delivery.
  • Impact of Reputation: Sender reputation significantly impacts soft bounce rates; poor reputation increases bounces.

Key considerations

  • Analyze Bounce Data: Carefully review bounce messages from your ESP to pinpoint specific reasons for failures.
  • List Hygiene: Regularly clean your email list to remove inactive or problematic addresses.
  • Content Optimization: Ensure your email content is relevant, engaging, and doesn't trigger spam filters.
  • Authentication Protocols: Implement SPF, DKIM, and DMARC to authenticate your emails and improve deliverability.
  • Sending Infrastructure: Properly configure your sending infrastructure to prevent server-side delivery issues.
  • Sending Volume: Maintain consistent and appropriate sending volumes to avoid being blacklisted.
  • Address Acquisition: Consider the age and acquisition method of email addresses; avoid sending to old or unengaged addresses.

What email marketers say
9Marketer opinions

Soft bounces indicate temporary email delivery issues, such as full mailboxes, server downtime, or graylisting. Resolving these involves identifying the bounce classification and origin, cleaning email lists, improving content relevance, ensuring proper email authentication (SPF, DKIM, DMARC), and monitoring sender reputation. Sending to engaged recipients and resolving immediate issues contribute to minimizing soft bounces.

Key opinions

  • Temporary Issues: Soft bounces are typically caused by temporary issues like full mailboxes, server problems, or graylisting.
  • List Hygiene: Maintaining a clean email list is crucial to reducing soft bounces.
  • Content Relevance: Relevant email content helps avoid triggering spam filters.
  • Authentication: Proper email authentication (SPF, DKIM, DMARC) improves deliverability.
  • Sender Reputation: Monitoring and maintaining a good sender reputation is essential.

Key considerations

  • Bounce Classification: Identify the specific classification and providers of soft bounces to diagnose the root cause.
  • Sending Volume: Maintain a consistent sending volume to avoid triggering graylisting.
  • Engagement: Focus on sending emails to engaged recipients to improve deliverability.
  • Email Size: Avoid sending overly large emails, as they can contribute to soft bounces.
  • Monitoring: Continuously monitor bounce rates and take prompt action based on feedback loops.
Marketer view

Email marketer from StackExchange explains that soft bounces mean a temporary issue occurred, such as a server being unreachable or a quota being exceeded. Resolving the immediate issues and following email best practices, like authenticating your domain, is recommended.

April 2021 - StackExchange
Marketer view

Email marketer from Reddit shares that soft bounces are often due to temporary problems like the recipient's server being down or their mailbox being full. To fix it, ensure your list is clean and that you are not sending overly large emails, and monitor your sending reputation.

March 2023 - Reddit
Marketer view

Email marketer from HubSpot explains that a soft bounce indicates a temporary delivery issue, such as a full inbox or a server problem. HubSpot recommends monitoring bounce rates and addressing underlying issues like poor list hygiene or content problems. Strategies include segmenting lists, improving content relevance, and authenticating emails.

January 2023 - HubSpot
Marketer view

Email marketer from Mailjet explains that soft bounces occur due to temporary issues like a full inbox, server downtime, or the recipient's server being overloaded. Mailjet retries delivery over a certain period. To fix soft bounces, ensure your email content is relevant, maintain a clean list, and authenticate your email.

March 2023 - Mailjet
Marketer view

Email marketer from Sendinblue shares that soft bounces can happen because of temporary problems such as the recipient’s mailbox being full, the server being down, or a large email size. To minimize soft bounces, clean up your email list, improve email content, and maintain a good sender reputation.

May 2022 - Sendinblue
Marketer view

Email marketer from MailerCheck shares that soft bounces are temporary problems that need regular list cleaning to ensure quality. Also, monitor email content that may trigger spam filters to affect sender reputation, which would then in turn increase soft bounces.

January 2022 - MailerCheck
Marketer view

Email marketer from Litmus responds that understanding soft bounces requires addressing temporary issues. Strategies should include cleaning mailing lists, improving sender reputation, and using proper authentication methods. Monitor bounce rates and promptly act on feedback loops.

August 2021 - Litmus
Marketer view

Email marketer from Email Geeks Forum shares that soft bounces indicate a temporary delivery problem, usually due to issues like a full inbox or server unavailability. Regularly clean your list and monitor your sender reputation to improve email delivery.

February 2023 - Email Geeks Forum
Marketer view

Marketer from Email Geeks shares that identifying the classification of soft bounces and the providers they originate from is the crucial initial step.

October 2023 - Email Geeks

What the experts say
4Expert opinions

Soft bounces are often temporary failures caused by various issues, including full mailboxes, server unavailability, or graylisting. Analyzing bounce messages from your ESP is crucial. Addressing infrastructure configuration, content triggering spam filters, sending frequency, recipient engagement, and implementing proper authentication methods (SPF, DKIM, DMARC) can help resolve soft bounces.

Key opinions

  • Temporary Failures: Soft bounces are primarily caused by temporary issues such as full mailboxes or server unavailability.
  • Graylisting: Graylisting, where servers temporarily reject mail from unknown senders, is a common cause of soft bounces.
  • Recipient Engagement: Sending to engaged recipients helps to minimize soft bounces.
  • Authentication: Proper authentication (SPF, DKIM, DMARC) reduces graylisting and improves deliverability.

Key considerations

  • Bounce Analysis: Review bounce messages from your ESP to understand the specific reasons for soft bounces.
  • Infrastructure Configuration: Ensure your sending infrastructure is properly configured to minimize delivery issues.
  • Content: Ensure your email content is not triggering spam filters.
  • Sending Practices: Maintain a consistent sending volume to avoid being blacklisted.
  • Address Age & Acquisition: Consider how old the addresses are, how frequently you send, and how they were acquired.
Expert view

Expert from Email Geeks explains that there are many reasons why email might temporarily fail to deliver. You should review messages returned by the sending server from your ESP and analyze the reason for the soft bounce.

November 2024 - Email Geeks
Expert view

Expert from Word to the Wise explains that graylisting is a common cause of soft bounces, where a receiving server temporarily rejects mail from an unknown sender. It recommends proper authentication (SPF, DKIM, DMARC), maintaining a consistent sending volume, and ensuring your IP address is not blacklisted.

March 2021 - Word to the Wise
Expert view

Expert from Email Geeks suggests collecting more information about the type of soft bounce, how frequently you send to these addresses, how old the addresses are, and what kind of engagement these addresses typically get. If the addresses are new, how were they acquired?

August 2022 - Email Geeks
Expert view

Expert from Spam Resource explains that soft bounces are often caused by temporary issues such as a full mailbox or a server being temporarily unavailable. Solutions include ensuring your sending infrastructure is properly configured, that your content is not triggering spam filters, and that you are sending to engaged recipients.

June 2022 - Spam Resource

What the documentation says
5Technical articles

Soft bounces, identified by 4xx SMTP response codes, are temporary email delivery failures often caused by issues like full mailboxes, DNS problems, or general server unavailability. Email service providers like Amazon SES, Exchange Online, SparkPost, and Twilio SendGrid automatically retry delivery for a defined period. Addressing underlying issues, monitoring bounce notifications, ensuring email relevance, keeping lists updated, and adhering to provider guidelines are crucial for resolving persistent soft bounces and preventing them from becoming hard bounces.

Key findings

  • Temporary Failure: Soft bounces represent temporary delivery failures, as indicated by 4xx SMTP response codes.
  • Automatic Retries: ESPs like Amazon SES, Exchange Online, SparkPost, and Twilio SendGrid automatically retry delivery for a certain period.
  • Potential for Hard Bounce: If the issue persists, a soft bounce can eventually turn into a hard bounce.

Key considerations

  • Underlying Issues: Address underlying issues like content problems or sender reputation to reduce soft bounces.
  • Bounce Monitoring: Monitor bounce notifications to identify and address issues promptly.
  • List Maintenance: Keep email lists updated and send relevant email to minimize bounces.
  • Provider Guidelines: Ensure your email practices comply with the guidelines of your email service provider (e.g., AWS).
  • SMTP Codes: Understanding SMTP response codes can aid in diagnosing email delivery issues.
Technical article

Documentation from Twilio SendGrid describes that soft bounces are temporary delivery failures and they will automatically attempt to resend for up to 72 hours. However, if the email isn't sent it may become a permanent bounce. To avoid this from happening, be sure to send relevant email and keep lists updated.

February 2024 - Twilio SendGrid
Technical article

Documentation from Amazon Web Services explains that Amazon SES handles soft bounces by attempting redelivery for a certain period. A soft bounce typically indicates a temporary issue, such as the recipient's mailbox being full. If the issue persists, the soft bounce might eventually turn into a hard bounce. Monitor bounce notifications and ensure your email practices comply with AWS guidelines.

March 2024 - Amazon Web Services
Technical article

Documentation from SparkPost explains that soft bounces are temporary delivery failures that require retries, which their system handles. Addressing underlying issues like content problems or sender reputation is vital for long-term resolution.

July 2022 - SparkPost
Technical article

Documentation from Microsoft explains that a soft bounce (or temporary failure) in Exchange Online indicates a transient issue such as a full mailbox or DNS problem. Exchange Online retries delivery for a period. Addressing issues like incorrect email addresses or server problems can reduce soft bounces.

October 2022 - Microsoft
Technical article

Documentation from RFC Editor explains that a soft bounce, or temporary failure, is indicated by a 4xx SMTP response code. These temporary failures suggest the email might be deliverable later. The sending server should retry delivery after a delay. Understanding SMTP response codes helps in diagnosing and addressing email delivery issues.

November 2021 - RFC Editor