Gmail Bounce Checker — Decode Your Bounce Messages
Got a Non-Delivery Report from Gmail? Use this guide to understand what the bounce code means, why your email was rejected, and the exact steps to fix it.
Common Gmail Bounce Codes
Every bounce message includes a numeric SMTP code and a sub-code. Find yours below.
550 / 5.1.1Recipient address does not existHard bounceWhat it means
The email address you are sending to does not exist on the receiving mail server. This is a permanent hard bounce.
What to do
Verify the email address is spelled correctly. If sending to a list, remove this address immediately — re-attempting will hurt your sender reputation.
550 / 5.7.1Message rejected by policy (spam)Hard bounceWhat it means
The receiving server rejected your message based on a content or policy filter. This often means your IP, domain, or message content triggered a spam rule.
What to do
Check if your sending IP or domain is on any blocklists (MXToolbox). Ensure SPF, DKIM, and DMARC are configured correctly. Review your email content for spam trigger words or excessive links.
421 / 4.7.0Temporary rate limitSoft bounceWhat it means
The receiving server is temporarily refusing connections because your sending rate is too high. Gmail uses this to throttle bulk senders.
What to do
Slow down your sending rate and retry after a delay. Spread large sends over longer time windows. If you send large volumes regularly, consider IP warming and dedicated sending infrastructure.
452 / 4.2.2Mailbox fullSoft bounceWhat it means
The recipient's mailbox has exceeded its storage quota. The server cannot accept new messages until space is freed.
What to do
This is a temporary condition on the recipient's end. Retry delivery after 24–48 hours. If the bounce persists over days, the account may have been abandoned.
550 / 5.5.0DMARC failureHard bounceWhat it means
Your email failed DMARC alignment checks. The receiving server verified that the From domain does not match your SPF or DKIM authentication.
What to do
Check your DMARC record (dig TXT _dmarc.yourdomain.com). Ensure your SPF record includes all legitimate sending IPs. Ensure your DKIM key is properly published and that your ESP signs with the From domain.
550 / 5.7.26DKIM failureHard bounceWhat it means
The DKIM signature in your email's header did not pass verification. This usually means the signature was tampered with in transit, the key is wrong, or no DKIM record exists.
What to do
Verify your DKIM public key is published as a TXT record at selector._domainkey.yourdomain.com. Check that your mail server is signing outgoing emails. Ensure no intermediate servers are modifying headers after signing.
Hard Bounces vs Soft Bounces
Hard Bounce
A permanent delivery failure. The receiving server has definitively rejected the message. Common causes: address does not exist, domain does not exist, DMARC/DKIM failure, spam policy rejection.
- Remove the address from your list immediately
- Do not retry — it will not work
- High hard bounce rate damages sender reputation
- SMTP codes: 5xx (e.g., 550, 551, 553)
Soft Bounce
A temporary delivery failure. The receiving server could not accept the message right now but the address is valid. Common causes: mailbox full, server temporarily unavailable, rate limiting.
- Retry delivery after 24–48 hours
- Most mail servers retry automatically
- If it persists for 5+ days, treat as hard bounce
- SMTP codes: 4xx (e.g., 421, 452, 451)
Frequently Asked Questions
- What does it mean when an email bounces?
- A bounce means your email was not delivered. The receiving mail server rejected the message and sent back a Non-Delivery Report (NDR) explaining why. There are two types: hard bounces (permanent — the address does not exist) and soft bounces (temporary — mailbox full or server unavailable).
- What is a Gmail NDR (Non-Delivery Report)?
- An NDR is an automated email sent back to you when a message cannot be delivered. It contains SMTP error codes, a description of the problem, and diagnostic information. Gmail NDRs include a numeric code (e.g., 550) and a sub-code (e.g., 5.1.1) that together pinpoint the exact reason for rejection.
- What does Gmail error 550 mean?
- Error 550 is a permanent rejection. The sub-code specifies the reason: 5.1.1 = address does not exist; 5.7.1 = policy rejection (spam); 5.5.0 = DMARC failure; 5.7.26 = DKIM failure. All 550 errors require investigation — simply resending will not work.
- Why are my emails going to spam instead of bouncing?
- When email goes to spam instead of bouncing, the server accepted the message but the spam filter classified it as junk. No NDR is generated. Common causes: missing SPF/DKIM/DMARC records, poor sender reputation, or spam-trigger content. Fix: authenticate your domain and improve your sender reputation over time.
- How can I reduce email bounce rate?
- Use double opt-in to verify addresses. Remove hard bounces immediately. Set up SPF, DKIM, and DMARC. Validate email addresses before adding them to your list. Send consistently rather than in sporadic large bursts. Keep bounce rates below 2% to maintain a healthy sender reputation.
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