Summary
Email deliverability distinguishes between hard and soft bounces, representing different types of delivery failures that require specific management strategies. A hard bounce signifies a permanent delivery failure, commonly due to an invalid or non-existent email address or domain. These unrecoverable errors necessitate immediate removal of the recipient from your mailing list to safeguard your sender reputation. Conversely, a soft bounce indicates a temporary delivery issue, such as a full inbox, a server being temporarily unavailable, or an oversized message. While email service providers typically attempt redelivery for soft bounces over a short period, consistent or recurring soft bounces from the same address should eventually be treated like hard bounces, leading to their removal to maintain list health and prevent long-term damage to deliverability. Effective bounce management involves diligent list hygiene, prompt suppression of hard bounces, and strategic monitoring of soft bounces.
Key findings
- Permanent vs. Temporary: Hard bounces indicate a permanent delivery failure, while soft bounces signal a temporary delivery issue that may resolve itself.
- Hard Bounce Causes: Common reasons for hard bounces include invalid or non-existent email addresses and domains, or recipient servers explicitly rejecting the address as invalid.
- Soft Bounce Causes: Soft bounces are typically caused by issues such as a full inbox, a temporarily unavailable server, or a message exceeding size limits, though auto-responders are not considered a bounce type by all experts.
- Immediate Hard Bounce Removal: Addresses that result in hard bounces must be immediately removed from mailing lists to protect sender reputation and deliverability.
- Soft Bounce Retries: Email service providers generally attempt to re-deliver emails that soft bounce for a short period, often up to three days.
- Persistent Soft Bounce Removal: If an email address consistently soft bounces over time, it should eventually be treated like a hard bounce and removed to prevent ongoing deliverability issues and reputation damage.
- Sender Reputation Impact: Both hard and unmanaged persistent soft bounces significantly impact a sender's reputation, potentially leading to future emails being blocked or sent to spam folders.
Key considerations
- Varying Definitions: Recognize that the terms 'hard bounce' and 'soft bounce' can be defined inconsistently across different email platforms and contexts. Some systems may categorize all non-delivery reasons, other than an explicit 'invalid address' reply, as soft bounces.
- Strategic Soft Bounce Management: While email service providers often automate retries for soft bounces, marketers should establish their own thresholds for when to remove an address that consistently soft bounces over a defined period, for example, after a certain number of consecutive bounces over several days or weeks.
- Re-engagement for New Signups: If a legitimate new signup occurs for an email address that previously bounced, consider selectively retrying sends to it for a limited period, as its previous bounce status might no longer be relevant.
- Proactive List Hygiene: Implement proactive strategies like double opt-in and regular list cleaning to minimize bounce rates from the outset, ensuring a healthier and more engaged email list.
- Monitoring and Automation: Utilize bounce notifications and automation features provided by your email service provider to efficiently track and process different bounce types, ensuring timely suppression of bad addresses and maintaining deliverability.
What email marketers say
12 marketer opinions
The difference between hard and soft email bounces lies in the permanence of the delivery failure. Hard bounces represent an irreversible inability to deliver an email, typically due to a non-existent address or domain, and require immediate removal from mailing lists to protect sender reputation. Soft bounces, conversely, indicate a temporary obstacle, such as a full inbox or server issues, which may resolve on their own. While email service providers often attempt redelivery for soft bounces, persistent occurrences from the same address necessitate its eventual removal, akin to a hard bounce, to maintain list hygiene and overall deliverability. Effective management hinges on prompt action against hard bounces and diligent monitoring of soft bounces.
Key opinions
- Hard vs. Soft Distinction: Hard bounces signify permanent email delivery failures, while soft bounces indicate temporary, often resolvable, delivery issues.
- Permanent Failure Causes: Hard bounces frequently result from invalid or non-existent email addresses, or domains that no longer exist.
- Temporary Obstacle Causes: Soft bounces are typically caused by factors like full inboxes, temporary server outages, or messages exceeding size limits. Some experts distinguish that auto-responders are not considered a bounce type.
- Immediate Removal for Hard Bounces: It is crucial to promptly remove email addresses that generate hard bounces to safeguard sender reputation and ensure email deliverability.
- Soft Bounce Retries by ESPs: Email service providers commonly attempt to re-send emails that initially result in soft bounces.
- Handling Persistent Soft Bounces: Addresses that consistently produce soft bounces over time should be treated similar to hard bounces and removed from mailing lists to prevent long-term deliverability issues.
- Impact on Sender Reputation: Both unaddressed hard bounces and recurring soft bounces can negatively affect sender reputation, potentially leading to emails being filtered into spam or blocked entirely.
Key considerations
- Varying Bounce Definitions: Be aware that the classification of 'hard' versus 'soft' bounces can differ across various email service providers and contexts.
- Custom Soft Bounce Thresholds: Marketers should define clear internal policies for when to remove addresses that repeatedly soft bounce, for instance, after a specific number of consecutive failures over a set period.
- Re-engagement with New Sign-ups: If a previously bounced address legitimately signs up again, it may be reasonable to attempt sending emails to it, as its status may have changed.
- Proactive List Health Measures: Employ proactive strategies like double opt-in and regular list cleaning to minimize bounce rates and maintain a healthy, responsive email list.
- Automated Bounce Management: Leverage automated tools within email platforms to efficiently track, categorize, and act on different bounce types, streamlining list hygiene.
Marketer view
Marketer from Email Geeks explains that a hard bounce means the address or domain don't exist, while a soft bounce indicates an inbox full, auto-responder, or other user-defined temporary reason.
21 Feb 2022 - Email Geeks
Marketer view
Marketer from Email Geeks shares that hard and soft bounce are ill-defined terms, often used differently in various contexts. He also advises that if a legitimate signup for an address occurs, its previous bounce status doesn't mean that you shouldn't give it another go. He suggests it's not unreasonable to retry bounces for a while, for instance, at least three consecutive bounces over at least 15 days, but emphasizes being selective about this approach.
29 Nov 2021 - Email Geeks
What the experts say
2 expert opinions
Email deliverability depends heavily on understanding the distinct natures of hard and soft bounces. Hard bounces represent unrecoverable delivery errors, such as a non-existent email address or domain, necessitating immediate and permanent removal from your mailing list to safeguard sender reputation. Conversely, soft bounces indicate transient delivery issues, like a full recipient mailbox or a temporarily offline server, allowing for subsequent delivery attempts. However, while temporary, recurrent soft bounces for the same address should ultimately lead to its suppression, similar to a hard bounce, to ensure list health and prevent long-term damage to deliverability.
Key opinions
- Bounce Type Distinction: Hard bounces signify permanent email delivery failures, whereas soft bounces indicate temporary, often resolvable, delivery issues.
- Permanent Failure Triggers: Reasons for hard bounces commonly include invalid or non-existent email addresses, or domains that are no longer active.
- Temporary Issue Causes: Soft bounces typically arise from factors such as a full inbox, a server being temporarily unavailable, or message size exceeding limits.
- Immediate Hard Bounce Action: Email addresses generating hard bounces require immediate removal from mailing lists to protect sender reputation and deliverability.
- Soft Bounce Retries & Strategy: While email service providers usually attempt retries for soft bounces, an address consistently soft bouncing should eventually be removed from the mailing list.
- Reputation Consequences: Failing to properly manage both hard bounces and persistent soft bounces can severely degrade a sender's reputation, leading to email blockage or spam folder placement.
Key considerations
- ESPs' Bounce Classification: Be aware that the categorization of 'hard' versus 'soft' bounces can vary across different email service providers and platforms.
- Establishing Soft Bounce Policies: Marketers should define specific internal thresholds for when to remove an email address that consistently generates soft bounces, for instance, after a set number of failures over a defined period.
- Re-engaging Previous Bounces: If an email address that previously bounced legitimately re-subscribes, it might be appropriate to attempt sending emails to it again, as its deliverability status may have changed.
- Proactive List Maintenance: Implement proactive list hygiene practices, such as employing double opt-in and regular list cleaning, to minimize bounce rates and maintain a healthy subscriber list from the start.
- Automated Bounce Handling: Leverage the automated bounce tracking and suppression features offered by email service providers to efficiently manage different bounce types and preserve deliverability.
Expert view
Expert from Spam Resource explains that hard bounces are permanent delivery failures, often due to an invalid email address or non-existent domain, requiring immediate removal from the mailing list to protect sender reputation. Soft bounces are temporary failures, like a full mailbox or unavailable server, which allow for retries; however, persistent soft bounces should eventually be treated as hard bounces and the address removed.
24 Jun 2022 - Spam Resource
Expert view
Expert from Word to the Wise shares that soft bounces indicate a temporary email delivery issue, such as a full mailbox or server problem, allowing for sender retries. In contrast, hard bounces signify a permanent failure, like an invalid or closed account, meaning no retries should occur, and the email address must be promptly removed from the mailing list to prevent sender reputation damage.
4 Sep 2024 - Word to the Wise
What the documentation says
4 technical articles
A fundamental aspect of email deliverability involves distinguishing between hard and soft bounces, each signaling a distinct type of delivery failure with specific management protocols. A hard bounce indicates a permanent, unrecoverable delivery failure, typically stemming from an invalid or non-existent recipient email address or domain. All major email service providers agree that addresses resulting in hard bounces must be immediately suppressed from mailing lists to preserve sender reputation. In contrast, a soft bounce signifies a temporary impediment, such as a full mailbox, a server being temporarily unavailable, or the message exceeding size limits. While ESPs generally attempt to re-deliver these emails for a period, recurrent soft bounces from the same address still warrant careful monitoring and eventual removal, as their persistence can negatively impact overall deliverability.
Key findings
- Bounce Type Distinction: Hard bounces represent permanent email delivery failures, whereas soft bounces indicate temporary, often resolvable, delivery issues.
- Hard Bounce Triggers: Common causes for hard bounces include invalid or non-existent email addresses and domains, leading to an irreversible delivery failure.
- Soft Bounce Factors: Soft bounces typically occur due to factors such as a full inbox, a server being temporarily unavailable, or a message exceeding size limits.
- Immediate Suppression: Addresses that generate hard bounces require immediate removal from mailing lists across all major platforms to protect sender reputation.
- ESPs Retry Soft Bounces: Email service providers generally attempt to re-send emails that initially soft bounce for a limited duration, such as up to three days.
- Managing Persistent Soft Bounces: Addresses that consistently soft bounce over time should be monitored and eventually removed, as their persistence can negatively impact overall deliverability, similar to a hard bounce.
- Reputation Impact: Both unmanaged hard bounces and recurring soft bounces can significantly degrade a sender's reputation, potentially leading to emails being blocked or filtered into spam.
Key considerations
- ESPs' Bounce Classification Nuances: Recognize that the specific categorization of 'hard' versus 'soft' bounces can vary slightly across different email service providers and platforms, even if the general principles are consistent.
- Defined Soft Bounce Removal Policies: Marketers should establish clear internal thresholds and timelines for when to remove email addresses that repeatedly generate soft bounces, as persistent issues can still harm sender reputation.
- Leverage Bounce Notifications: Utilize the bounce notification features offered by email service providers to promptly identify and act on different bounce types, ensuring timely list hygiene and reputation protection.
- Proactive List Hygiene: Implement proactive strategies like double opt-in and regular list cleaning to minimize bounce rates from the outset, contributing to a healthier and more engaged email list.
- Automated Management Tools: Employ the automated bounce processing and suppression tools provided by email platforms for efficient management of different bounce types and the preservation of deliverability.
Technical article
Documentation from Mailchimp explains that a hard bounce is a permanent delivery failure due to reasons like an invalid or non-existent email address, and Mailchimp automatically removes these addresses from lists. A soft bounce is a temporary issue, such as a full inbox or server timeout, and Mailchimp will retry sending for up to 3 days, converting the bounce to a hard bounce if delivery remains unsuccessful. Hard bounces significantly impact sender reputation, so immediate removal is crucial, while soft bounces require monitoring and eventual removal if they persist.
13 Aug 2023 - Mailchimp
Technical article
Documentation from SendGrid explains that a hard bounce indicates a permanent failure, meaning the email address is invalid or the domain does not exist, and should be immediately suppressed to protect sender reputation. A soft bounce signifies a temporary delivery issue, such as a full inbox, a server being temporarily unavailable, or the message being too large. SendGrid retries soft bounces and advises senders to monitor recurring soft bounces, considering removal if they become persistent, as many soft bounces can still harm deliverability.
8 May 2025 - SendGrid
How does Salesforce Marketing Cloud handle email bounces and what are the best practices for bounce management?
How should different bounce types be classified and handled by ESPs?
How to parse SMTP responses to identify hard and soft bounces?
What are the best practices for managing hard and soft bounces in daily email campaigns?
What causes soft bounces for a single contact and how should they be handled?
What types of email bounces should be eliminated and which should be monitored?
