Summary
Soft bounces for a single contact are generally caused by temporary issues such as full mailboxes, server outages, or email size limitations. More specific issues like misconfigured on-premise Exchange servers or O365 email forwarding with content filtering can also contribute. The recommended approach is to initially allow the system to retry sending the email. However, if soft bounces persist for a specific contact, it is strongly advised to remove that contact from the mailing list to protect sender reputation and maintain overall email deliverability. Monitoring bounce rates is also crucial for proactively addressing deliverability issues.
Key findings
- Common Temporary Causes: Full mailboxes, server outages, and email size limitations are common causes of soft bounces.
- Specific Configuration Issues: Misconfigured Exchange servers or O365 forwarding with content filtering can lead to soft bounces for individual contacts.
- Automatic Retries: Most email systems automatically retry sending emails that soft bounce.
- Reputation Protection: Removing persistently soft-bouncing contacts protects sender reputation and maintains deliverability.
- Importance of Monitoring: Monitoring bounce rates enables proactive identification and resolution of deliverability problems.
Key considerations
- Initial Retry Period: Allow sufficient time for the system to automatically retry sending emails before taking further action.
- List Hygiene Practices: Implement and maintain regular list cleaning practices to remove contacts with consistently high soft bounce rates.
- Threshold for Removal: Establish a clear threshold for the number of soft bounces before removing a contact from the list.
- Investigate Specific Issues: If possible, investigate specific configuration issues (e.g., Exchange server problems, O365 forwarding) for persistently soft-bouncing contacts.
- Long-Term Impact: Recognize and address the long-term impact of persistent soft bounces on sender reputation and overall deliverability.
What email marketers say
11 marketer opinions
Soft bounces for a single contact are typically caused by temporary issues like a full mailbox, server problems, or email size limits. These issues may be specific to that contact, such as a misconfigured on-premise Exchange server. The general consensus is to retry sending the email a few times, but if soft bounces persist, the contact should be removed from the mailing list to protect sender reputation and avoid further deliverability issues. Monitoring soft bounce rates is also crucial for adjusting sending practices.
Key opinions
- Common Causes: Soft bounces are usually caused by temporary issues like a full inbox, server problems, or email size limits.
- Contact-Specific Issues: Some soft bounces might be due to issues specific to the recipient's configuration, such as a misconfigured on-premise Exchange server.
- Handling Soft Bounces: Email systems often automatically retry delivery for soft bounces.
- Persistent Soft Bounces: Contacts with persistent soft bounces should be removed from the mailing list to avoid damaging sender reputation.
- Monitoring: Monitoring soft bounce rates is important for identifying and addressing deliverability issues.
Key considerations
- Retry Attempts: Allow the system to retry sending emails that soft bounce.
- List Hygiene: Regularly clean your email list by removing contacts who consistently soft bounce.
- Reputation Impact: Persistent soft bounces can negatively impact your sender reputation, so proactive management is essential.
- Domain vs. Contact: If bounces are only occurring with a single contact and not the entire domain, isolate and address that specific contact.
Marketer view
Email marketer from Mailchimp explains that a soft bounce indicates a temporary delivery issue, such as a full inbox, a server problem, or the email size. Mailchimp automatically handles some soft bounces by retrying delivery, but persistent soft bounces should be removed from your list to avoid deliverability issues.
24 Sep 2021 - Mailchimp
Marketer view
Email marketer from Email Marketing Forum User mentions that soft bounces are usually caused by a full inbox or temporary server issues. The user recommends trying to resend the email a couple of times, but if the soft bounce persists, it’s best to remove the address to protect your sender reputation.
1 Dec 2024 - Email Marketing Forum
What the experts say
2 expert opinions
Soft bounces for a single contact can stem from various underlying issues. One potential cause is an O365 system configured to forward emails to another service, which then blocks the message due to a content filter, resulting in a mail loop. Other reasons for soft bounces include a full mailbox, greylisting, or temporary server outages. While soft bounces are usually temporary, persistent issues from a specific address often indicate a need for list cleaning to maintain a good sending reputation.
Key opinions
- Mail Loop in O365: O365 systems configured to forward emails to other services with content filters can cause mail loops and soft bounces.
- Common Soft Bounce Causes: Soft bounces may arise from full mailboxes, greylisting, or temporary server outages.
- Persistent Soft Bounces: Consistent soft bounces from a specific email address may signal a persistent issue requiring list cleaning.
Key considerations
- Investigate O365 Forwarding: If encountering soft bounces with O365 users, investigate whether their email is being forwarded to another service with filtering.
- Monitor Bounce Frequency: Pay attention to the frequency of soft bounces from a specific email address to identify potential persistent issues.
- List Maintenance: Practice regular list cleaning to remove email addresses that consistently result in soft bounces to maintain a good sending reputation.
Expert view
Expert from Email Geeks shares that the underlying issue can be that the O365 system was configured to forward to something else - and that something else was using a filter that blocked the message and so sent back to O365 and then it ended up in a loop. If it was a content-based filter, that would explain why only some of the messages bounced - those messages were content blocked and the others weren’t. Mentally she treats mail loops from Outlook as a downstream mail block.
11 Jun 2024 - Email Geeks
Expert view
Expert from Word to the Wise, Laura Atkins, explains that soft bounces can result from various issues like full mailboxes, greylisting, or temporary server outages. She suggests that these are generally temporary problems, and the server will often retry. However, consistent soft bounces from a specific address indicate a more persistent issue, potentially requiring list cleaning to maintain a good sending reputation.
27 Oct 2023 - Word to the Wise
What the documentation says
5 technical articles
Documentation across multiple sources (MailerQ, Amazon SES, Postmark, SparkPost, and Google) indicates that soft bounces are caused by temporary issues, such as a full mailbox, server downtime, or oversized messages. All sources suggest retrying the email delivery initially. However, they uniformly advise that persistent soft bounces should be treated as hard bounces, with the problematic email address removed from the list to protect the sender's reputation and maintain deliverability.
Key findings
- Temporary Issues: Soft bounces are primarily caused by temporary problems like full mailboxes or server unavailability.
- Automatic Retries: Email service providers often automatically retry sending emails that initially soft bounce.
- Reputation Impact: Repeated soft bounces can negatively impact sender reputation and overall deliverability.
- List Hygiene: Removing email addresses that consistently result in soft bounces is essential for maintaining a healthy email list.
Key considerations
- Retry Strategy: Allow the system to automatically retry sending emails that soft bounce initially.
- Monitor Bounce Rates: Actively monitor soft bounce rates to identify potential deliverability issues.
- Removal Threshold: Establish a threshold for the number of soft bounces before removing an email address from the list.
- Sender Reputation: Prioritize sender reputation by proactively managing soft bounces.
Technical article
Documentation from Postmark explains that soft bounces are temporary failures like a full inbox or a server issue. Postmark suggests automatically retrying emails that soft bounce but recommends removing contacts who repeatedly soft bounce to maintain good deliverability.
14 Aug 2021 - Postmark
Technical article
Documentation from SparkPost explains that soft bounces are temporary delivery failures, often due to a full mailbox or temporary server issues. SparkPost's system retries these emails, but recommends that senders monitor their soft bounce rates and remove addresses that persistently soft bounce to preserve sender reputation.
1 Apr 2025 - SparkPost
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