Soft bounces
What are email bounces?
Bounces occur when an email is returned to the sender without being delivered to the recipient. They're undesirable, affect your emails' deliverability, and should be kept below 2%.Bounces are classified into two types: hard and soft bounces. Hard bounces occur because of permanent, irreversible reasons, while soft bounces occur due to temporary issues.
This page gives a primer on hard bounces.
What are soft bounces?
A soft bounce occurs when an email reaches the recipient server, but can't be delivered to the inbox due to temporary reasons. Email service providers usually retry a few times before marking it as a hard bounce. Although less severe than a hard bounce, frequent soft bounces can signal issues with your recipient list and can affect overall deliverability.
Soft bounces vs. Hard bounces
Soft bounces | Hard bounces |
| Occur due to temporary issues, like full recipient inboxes, large email sizes, or server issues. | Occur due to permanent issues such as fake or incorrect addresses or non-existant domains. |
| Typically resolve on their own. | Don't resolve on their own. |
| Email can be retried. | Email cannot be retried; the address should be added to the suppression list. |
Causes of soft bounces
- Mailbox-related issues: Occurs when the mailbox is full, isn't configured correctly, or is inactive.
- Message size: Occurs when the email—including attachments—exceeds the recipient's size limit.
- DNS failure: Occurs when the DNS is misconfigured or the server is temporarily offline.
- Connectivity issues: Occurs when the sending server can't connect with the recipient due to temporary network connection issues.
- Greylisting: Some email servers might reject emails from new senders to avoid spam attempts. However, if the sender retries, the email is usually delivered.
- Rate limiting: Recipient servers often have limits on how many emails they accept in a given time period. Emails sent beyond this cap are temporarily rejected until the limit resets.
Best practices to handle soft bounces
- Keep an eye on email size. Make sure the complete email, including attachments, falls within the recipient server's maximum limit.
- Monitor your reports regularly to avoid email addresses that encounter frequent soft bounces.
- Choose an email service provider that has high uptime and ensures regular retries, since soft bounces usually resolve on their own.
- Authenticate domains using SPF, DKIM, and DMARC to signal you're a credible source and prevent bounces.
- Warm up outgoing emails gradually to avoid throttling.
- Separate transactional and marketing email streams to prevent one's reputation from affecting the other.