Common causes
- The recipient’s mailbox is full.
- The receiving server is down or overloaded.
- The email is too large.
- The receiving provider is temporarily limiting how many messages it accepts from your server.
What to do about soft bounces
Most email platforms retry soft bounces automatically for a few days. If the same address soft-bounces several campaigns in a row, treat it like a hard bounce and remove or suppress it, because repeated failures also hurt your sender reputation.
Soft bounce example
A company sends a newsletter to 5,000 people. 40 emails soft bounce: 25 because the mailbox is full, 10 because the recipient’s server was temporarily down and 5 because the message was held back by the provider. The email tool retries for 72 hours, and 32 of them are delivered. Eight addresses soft bounce again in the next two campaigns and are suppressed.
How to handle soft bounces
- Let your email platform retry automatically, which is the default.
- Look at the bounce report for patterns by domain. A whole provider bouncing can mean a block on your sending address.
- If an address soft-bounces in several campaigns in a row, suppress it.
- Reduce the size of messages with heavy images.
- Check your sender reputation and authentication if soft bounces rise suddenly.
Soft bounce mistakes
- Removing addresses at the first soft bounce and losing valid contacts.
- Never removing repeat soft bounces, which hurts reputation.
- Mixing up soft and hard bounces in reports.
Soft bounce FAQs
What is the difference between soft and hard bounces?
A soft bounce is temporary. A hard bounce is permanent.
Do soft bounces affect deliverability?
Repeated failures can. See email lists and email marketing.
Soft bounce reasons you can read in the report
Email platforms usually record the reason the receiving server gave, such as “mailbox full”, “message too large” or “temporarily deferred”. Group these reasons in your reports. A cluster of “deferred” messages to one provider usually points to a sending limit, while “mailbox full” is the recipient’s problem and often clears on its own. Looking at the reason before you act stops you from removing good contacts.
When to contact your email provider
If soft bounces climb above their usual level for several sends, or all of them come from one big mailbox provider, ask your sending platform to check your sending reputation and authentication records. Slowing the send and cleaning the list usually helps.