# Hard Bounce vs Soft Bounce

> A hard bounce is a permanent delivery failure, like an address that doesn't exist. A soft bounce is temporary, like a full mailbox. How to tell them apart by SMTP code, what to do about each, and the bounce rates that get sending paused.

Source: https://sendbroadcast.net/hard-bounce-vs-soft-bounce

A bounce is an email the receiving server refused to deliver. A **hard bounce** is permanent: the address doesn't exist or will never accept your mail. A **soft bounce** is temporary: the mailbox is full, the server is down, or it is slowing you down. You stop mailing hard bounces right away. Soft bounces usually clear up on their own.

## The difference at a glance

|  | Hard bounce | Soft bounce |
| --- | --- | --- |
| What it means | Delivery will never succeed | Delivery failed this time |
| SMTP code | 5xx, for example 550 5.1.1 | 4xx, for example 421 or 452 |
| Common causes | Mistyped or deleted address, domain that doesn't exist, permanent block | Full mailbox, server down, rate limiting, message too large |
| What to do | Suppress the address immediately | Let the sending service retry; suppress it if it keeps bouncing |

## Hard bounces

A hard bounce comes back with a 5xx SMTP status. The most common is `550 5.1.1`, meaning the mailbox doesn't exist. Others include a domain with no mail server, or a receiving server that has permanently blocked you.

Every further email to a hard-bounced address is wasted, and mailbox providers read repeated attempts as a sign that you don't clean your list. Good email software adds the address to a suppression list the first time it hard-bounces, so it is never mailed again.

The usual source of hard bounces is the list itself: typos at sign-up, old addresses from a long-dormant list, or addresses that were never real. Double opt-in stops most of them before they reach your list, because a mistyped address never confirms.

## Soft bounces

A soft bounce comes back with a 4xx status. The receiving server is saying "not now". Typical reasons are a full mailbox, a server that is temporarily unavailable, greylisting of an unknown sender, or throttling because you are sending too fast.

Your sending service retries soft bounces for a while, often up to a day or more, before giving up. Most are delivered on a later attempt. An address that soft-bounces on send after send, like a mailbox that has been full for months, should be treated as a hard bounce and suppressed.

A sudden wave of soft bounces from one provider, like many 421 responses from Microsoft or Gmail, usually isn't about the addresses. It means that provider is throttling you. Slow down, and check your authentication and complaint rate.

## Bounce rates to stay under

- **Under 2%** is healthy for a list you mail regularly.
- **Amazon SES** reviews accounts with a bounce rate of 5% or more, and can pause sending at 10%. For complaints, the review starts at 0.1% and pausing at 0.5%.
- **Gmail** asks bulk senders to keep spam complaints under 0.1% and never reach 0.3%.

A high bounce rate on the first send to an imported list is common. Clean the list before you import it, and send to your most recent, most engaged subscribers first.

## How Broadcast handles bounces

Broadcast receives bounce and complaint notifications from your sending service through its webhooks. A hard bounce or a complaint adds the address to the suppression list automatically, so it isn't mailed again from any channel it applies to. The broadcast's activity table shows the bounce reason for each recipient. See [how to handle bounces and delivery failures](/how-to/bounces-and-delivery-failures) for the steps inside Broadcast.

## Frequently asked questions

### What is the difference between a hard bounce and a soft bounce?

A hard bounce is permanent, usually an address that doesn't exist. A soft bounce is temporary, like a full mailbox or a busy server. Stop mailing hard bounces. Soft bounces are retried and usually delivered.

### Should I remove soft bounces from my list?

Not after one. Remove or suppress an address that soft-bounces repeatedly across several sends.

### Does a hard bounce hurt my sender reputation?

A few don't. A high hard bounce rate does, because it suggests an old or bought list. Keep it under 2%.

### What does 550 5.1.1 mean?

The recipient's mailbox doesn't exist. It is a hard bounce. Suppress the address.

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## Related

- [How to handle bounces in Broadcast](/how-to/bounces-and-delivery-failures)
- [Why your emails land in spam](/how-to/emails-going-to-spam)
- [Double opt-in, explained](/blog/double-opt-in-email-marketing)
- [Free email deliverability test](/tools/free-email-deliverability-test)