# Why are my cold emails bouncing, and how do I lower the bounce rate?

Canonical: https://growfast.sh/solutions/why-do-cold-emails-bounce | Last updated: 2026-11-13 | Published by GrowFast

Cold emails bounce because the mailbox does not exist, the domain has no mail server, the mailbox is full or unmonitored, or the receiver refuses your mail. Fix it by mailing only published addresses, checking MX records, avoiding role addresses like hello@, and removing hard bounces at once. In our own week, 5 of 160 emails bounced, four to hello@ or contact@.

## Why it happens

A bounce is a delivery failure notice sent back to you. Hard bounces are permanent: the address is wrong or the domain cannot receive mail. Soft bounces are temporary: a full mailbox, a busy server, or a receiver deferring you. Receivers watch your bounce rate because spammers send to lists full of dead addresses, so a high rate marks you as one.

The cause is almost always the list, not the email body. Guessed addresses, old contacts, role mailboxes and typos produce hard bounces. A second cause is the receiver rejecting you on policy, for example because your domain is not authenticated, which shows up as a 5.7.x code rather than a missing mailbox.

## The fix that works without GrowFast

1. **Read the code in the bounce message.** The first digit says what to do: 4.x.x is a temporary failure that may succeed later; 5.x.x is permanent and needs a change. 5.1.1 means the mailbox does not exist; 5.1.2 means the destination domain cannot take mail.
2. **Remove every hard bounce immediately.** Take the address off the list and add it to your suppression list so no later campaign writes to it.
3. **Look for patterns.** Group bounces by address type, domain, and the source of the list. One bad source or one address type often explains most of them.
4. **Check the domain receives mail.** dig MX company.com +short. No answer means no mail server; drop the domain.
5. **Stop mailing role addresses.** info@, hello@, contact@ and support@ are shared or unattended more often than named mailboxes.
6. **If the code is 5.7.x, check authentication.** Google rejects unauthenticated mail with a 5.7.26 error. Verify SPF, DKIM and DMARC for the sending domain.
7. **If you see 4.7.28 or deferrals, slow down.** Google says to pause for at least ten minutes, find the cause, then increase volume gradually.
8. **Re-verify old lists before reuse.** People leave companies and domains lapse. Re-check addresses older than a few months.

**Our own sending in the week to 23 October 2026 (small sample, one company, not a benchmark)**

| Result | Count |
| --- | --- |
| Sent | 160 |
| Delivered | 151 |
| Bounced | 5 (3.1%), four of them to hello@ or contact@ |
| No delivery status yet | 4 |
| Replies | 0 |

## How to read a bounce code

RFC 3463 defines the structure class.subject.detail. The class is 2 for success, 4 for a persistent transient failure and 5 for a permanent failure. The subject narrows the source, for example 1 for the address and 2 for the mailbox, and the detail gives the exact condition. The bounce text from the receiving server often adds a plain sentence; read it.

- 5.1.1: the mailbox in the address does not exist. Remove it.
- 5.1.2: the destination system does not exist or cannot accept mail. Remove the domain.
- 4.2.2: the mailbox is full, a temporary condition. Retry later, then give up.
- 5.7.x: a policy or authentication refusal. Fix the sender side, not the list.

## When to use GrowFast

GrowFast checks that a recipient's domain has a mail server before sending, drops service and generic inboxes, and suppresses anyone who bounced, unsubscribed or complained on any GrowFast account. A run pauses on its own if its list starts bouncing, and an account whose last 14 days bounced above 5% (with at least 20 results) is paused until those results age out. export_outreach returns every recipient with delivery status, so you can group bounces by address type.

**When it is not the right tool:** GrowFast cannot prove a mailbox exists, so some bounces will still happen. If your list came from somewhere you cannot defend, clean or replace it; no sending setting fixes that.

## Ask your AI assistant

Paste this into an assistant that has the GrowFast MCP server connected:

> Assign to GrowFast: export my outreach history (export_outreach), count delivered, bounced and replied by address type (named person, hello@, contact@, info@, other) and tell me which type bounces most. Don't send anything. Show me the numbers so I can approve changes to my list rules.

Tools used: `export_outreach`. These need the full server (https://growfast.sh/api/mcp) with an API key.

## FAQ

### What is a normal cold email bounce rate?

We do not have a benchmark we can source. Aim for as close to zero as your list allows. GrowFast pauses an account whose recent bounces exceed 5%, which is a ceiling, not a target.

### Is a soft bounce a problem?

A single one is not. Repeated soft bounces to the same address mean treat it as dead and stop.

### Do bounces hurt the person I emailed?

No, they hurt the sender: mailbox providers score your domain on bounces and complaints.

### Should I retry a bounced address?

Retry only 4.x.x failures, a few times over a day or two. Never retry a 5.1.1.

## Sources

- [RFC 3463, Enhanced Mail System Status Codes](https://www.rfc-editor.org/rfc/rfc3463) (read 2026-11-13)
- [Google, Email sender guidelines (Gmail Help)](https://support.google.com/mail/answer/81126) (read 2026-11-13)
- [GrowFast blog, Cold email bounce rate: hello@ vs named person (2026-10-23)](https://growfast.sh/blog/cold-email-bounce-hello-vs-named-person) (read 2026-11-13)

## Related

- [How do I find the right person's email at a company without guessing the address?](https://growfast.sh/solutions/find-decision-maker-email-without-guessing)
- [How do I clean my own lead list before sending cold email?](https://growfast.sh/solutions/clean-your-lead-list-before-cold-email)
- [How do I check that SPF, DKIM and DMARC are set up before I send cold email?](https://growfast.sh/solutions/check-spf-dkim-dmarc-before-cold-email)
- [Our bounce numbers in full](https://growfast.sh/blog/cold-email-bounce-hello-vs-named-person)
- [All problems and solutions](https://growfast.sh/solutions)