Soft Bounce
A soft bounce is a temporary email delivery failure. Learn common causes, how it differs from a hard bounce, and how to handle retries.
A soft bounce is a temporary email delivery failure. The recipient address may be valid, but the message could not be delivered at that moment because of a full mailbox, a temporary server issue, a message-size problem, or a receiving system delay.
Unlike a hard bounce, a soft bounce does not always mean the address is bad. It means the send failed for now and should be retried or monitored.
Soft bounce vs hard bounce
Bounce type | Meaning | What to do |
|---|---|---|
Soft bounce | Temporary delivery failure | Retry, monitor, then suppress if repeated |
Hard bounce | Permanent delivery failure | Suppress the address immediately |
The hard part is deciding when repeated soft bounces should become a suppression decision. A single soft bounce is normal. Repeated soft bounces from the same address or domain are a warning sign.
Common causes of soft bounces
Full mailbox. The recipient's inbox has no room for new mail.
Temporary receiving-server issue. The destination mail server is down, slow, overloaded, or unavailable.
Message too large. The email is too large for the receiving server's limits.
Temporary filtering. The receiving system delays or defers the message while it checks sender reputation or content.
Rate limiting. The receiving domain throttles messages because volume changed too quickly.
DNS or routing delay. Temporary domain or mail-routing issues can cause delivery to fail and later recover.
How to handle soft bounces
Retry with backoff. Do not immediately give up after one temporary failure. Retry in a controlled way rather than blasting repeated attempts.
Watch repeated failures. If the same address soft bounces multiple times, suppress it or move it into a re-verification workflow.
Segment by domain. If many addresses at one domain soft bounce, the issue may be domain-level throttling or server trouble, not individual addresses.
Check message size and content. Large images, heavy HTML, broken formatting, or suspicious links can contribute to temporary rejection.
Avoid sudden volume jumps. New domains and IPs need steady volume. Spikes can trigger throttling and temporary deferrals.
Protect transactional flows. If an account-critical email soft bounces repeatedly, create a user-facing recovery path in the product.
Examples
Full inbox
The address is valid, but the mailbox cannot receive new mail until space is cleared.
Temporary server outage
The receiving server is unavailable during the first attempt, then accepts a later retry.
Domain throttling
A receiving domain temporarily defers a batch because volume increased too quickly.
Oversized message
An email with heavy images or attachments exceeds the recipient server's size limit.
How soft bounces affect deliverability
Soft bounces are not as severe as hard bounces, but repeated soft bounces still matter. They can signal volume spikes, content problems, poor list quality, or domain-level throttling.
For SaaS teams, the practical question is whether the user is still reachable. If a receipt, password reset, or invite soft bounces repeatedly, the product may need to ask the user for a different address or show an account warning.
Loops helps teams manage bounce handling while keeping transactional, lifecycle, and marketing email connected to one contact model. Related reading: hard bounce, email deliverability, transactional emails, and email API.
FAQ
What is a soft bounce?
A soft bounce is a temporary email delivery failure. The address may be valid, but the message could not be delivered at that moment.
What causes soft bounces?
Common causes include full mailboxes, temporary server issues, message-size problems, temporary filtering, rate limiting, and DNS or routing delays.
Should I remove soft bounces immediately?
Not after one soft bounce. Retry and monitor. If an address soft bounces repeatedly, suppress it or ask the user to verify a different address.
How is a soft bounce different from a hard bounce?
A soft bounce is temporary and may resolve. A hard bounce is permanent and should be suppressed immediately.
Do soft bounces hurt deliverability?
Occasional soft bounces are normal. Repeated or domain-wide soft bounces can signal deliverability problems and should be investigated.
How can I reduce soft bounces?
Avoid sudden volume spikes, keep messages lightweight, authenticate your sending domain, monitor bounce patterns by domain, and keep contact data clean.