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Bounced Emails

Updated Oct 4, 2024

In this lesson…

Having Trouble With High Bounce Rates?

What is a Bounce Rate?

Bounce rate in email marketing refers to the percentage of emails that are not successfully delivered to recipients. Bounce rates can vary significantly depending on various factors, including the business, industry, frequency of sending broadcasts, the source of the contacts, and more. There are two types of bounces to understand:

  • Hard Bounces: Permanent delivery failures. These occur when the email address is invalid, doesn't exist, or the recipient's server has blocked your email.

  • Soft Bounces: Temporary delivery failures. These can happen if the recipient's mailbox is full, the server is down, or the message is too large.

What Bounce Rates are Considered Bad?

While acceptable bounce rates can vary depending on the industry and the quality of the email list, here are general guidelines:

  • Low Risk: Bounce rate below 2%

  • Moderate Risk: Bounce rate between 2% and 5%

  • High Risk: Bounce rate above 5%

Why High Bounce Rates are Problematic

High bounce rates can lead to several deliverability issues, including:

  • Damage to Sender Reputation: Email service providers (ESPs) use bounce rates to gauge the quality of your email list. High bounce rates can damage your sender reputation, making ESPs more likely to mark your emails as spam or block them entirely.

  • Increased Spam Filter Triggers: ESPs and email clients may categorize your emails as spam if they consistently encounter high bounce rates from your domain.

  • Blacklist Risk: Consistently high bounce rates can lead to your domain or IP address being blacklisted by ESPs and spam filter services, significantly impacting your ability to reach recipients.

  • Decreased Engagement: A high bounce rate indicates poor list hygiene, meaning many of your emails aren't reaching intended recipients. This results in lower open and click-through rates, reducing overall engagement.

What Does Simplero Do to Help? 

Simplero manages your contacts differently behind the scenes depending on whether we record a hard bounce or a soft bounce. 

Soft Bounces: When an email bounces for temporary reasons (e.g., connection errors, full inbox, domain setup issues), Simplero will notify you in the broadcast and contact records. However, these contacts will not be unsubscribed from your list.

Hard Bounces: If an email hard bounces (e.g., the email address doesn't exist or the domain is invalid), the contact will remain on your list but will be excluded from future mailings until the bounce status is resolved.

Repeated Bounces: If a contact's email soft bounces three consecutive times, Simplero will mark the contact as bounced, and they will be excluded from all mailing lists. We will reset the bounced status of contacts we record activity from. For example if they sign up to a list or make a purchase using the previously bounced email address.

We take email deliverability very seriously at Simplero. In addition to our responses to bounced contacts, the support team keeps an eye on bounce rates and spam complaints.

If your bounce rates go over 5% on a single email or overall for the month, our support team gets notified. We do this to ensure optimal performance for everyone using Simplero.

Here's why this matters:

  • Deliverability Protection: Spam and bad sender reputations can mess with email deliverability for everyone in the same sender pool.

  • Manual Monitoring: Our team manually checks bounce rates and spam activities to catch any issues early.

  • Taking Action: If problems come up, we might temporarily limit how many emails you can send. We'll then work closely with you to fix the issue.

These steps help us keep email deliverability high for all our users.

How to Mitigate Bounce Rates

Regularly Clean Your Email List: Update or remove invalid and outdated email addresses.

Filter Contacts:

  • Use the "Email Bounced" filter in your contacts table to identify contacts with hard bounces.

 Resetting Bounce Flags:

  • If a contact's email has been restored or updated and is now valid, reset the bounce flag on the contact record.

Unsubscribing or Deleting Contacts:

  • If a contact's email remains invalid, unsubscribe them from all lists: 

  • Or delete the contact if applicable: 

Use Double Opt-In: Ensure that recipients confirm their subscription to reduce the chances of incorrect email entries. (Found in list settings >> configure tab) 

Monitor Bounce Reports: Regularly check bounce reports to identify and address issues promptly.

By maintaining a low bounce rate, you can improve your email deliverability, ensure better engagement, and maintain a positive sender reputation.

Bounce Message Glossary and How to Handle Them

View your bounce messages from your broadcast delivery reports. Open the broadcast summary and click See Who next to the bounce stat. 

That will open to a list of all of your bounce messages: 

Below is a list of common bounce messages along with troubleshooting tips. If you find anything missing from the list, please let us know, and we will add it.

Common Bounce Messages

Other Bounce Codes

554 Message not allowed - [299]

  • Meaning: The content of the message violates email policies (e.g., objectionable links, malicious attachments, or bad header information).

  • Solution: Review the email content for anything that might be flagged as spam or inappropriate. Adjust the content and try resending.

451 Message temporarily deferred

  • Meaning: This error indicates a temporary problem blocking the delivery of your message, often due to unusual traffic patterns or spam characteristics.

  • Solution: Wait and try resending the email later. If the issue persists, contact your email service provider for further assistance.

554 5.2.2 Mailbox full

  • Meaning: The recipient's mailbox is full and cannot accept new emails.

  • Solution: The recipient should delete unnecessary emails or increase their mailbox quota.

Error dialing remote address…

  • Meaning: There was a problem connecting to the recipient's email server, possibly due to network issues or incorrect server configuration.

  • Solution: Check your network connection and ensure the recipient's email address and server details are correct.

Unable to get MX info…

  • Meaning: The email server was unable to retrieve the Mail Exchanger (MX) records for the recipient's domain, which are necessary for routing the email.

  • Solution: Verify the recipient's email address for any typos. If the address is correct, check the DNS settings for the recipient's domain.

452 4.2.2 Quota exceeded

  • Meaning: The recipient's mailbox has exceeded its storage quota.

  • Solution: The recipient should delete unnecessary emails or increase their mailbox quota if possible.

554 5.4.7 [internal] Exceeded max time without delivery

  • Meaning: The email has been in the delivery queue for too long without being delivered.

  • Solution: Consider resending the email later or contacting the recipient to ensure their email server is functioning correctly.

451 4.4.0 Proxy failed

  • Meaning: There was a temporary failure with a proxy server during the email delivery process.

  • Solution: Try resending the email later. If the issue persists, contact your email service provider for assistance.

554 5.4.4 [internal] Domain lookup failed

  • Meaning: The recipient's domain could not be found or resolved.

  • Solution: Verify the recipient's email address for any typos. If the address is correct, check the DNS settings for the recipient's domain.

550 Relay not permitted

  • Meaning: The sender's email server is not allowed to relay the message through the recipient's email server.

  • Solution: Check your email server settings to ensure it is authorized to send emails through the recipient's server. This might involve configuring SMTP authentication or adjusting relay settings.

554 5.4.14 Hop count exceeded - possible mail loop

  • Meaning: The email has passed through too many mail servers (hops) without being delivered, indicating a possible mail loop.

  • Solution: Check your email routing settings to ensure there are no misconfigurations causing a mail loop. Adjust the configuration to prevent excessive hops.

550 5.1.1 User unknown

  • Meaning: The recipient's email address does not exist on the recipient's email server.

  • Solution: Verify the recipient's email address for any typos or errors. If the address is correct, contact the recipient through another means to confirm their email address.

550 5.1.2 Bad destination system address

  • Meaning: The domain name in the recipient's email address is invalid or does not exist.

  • Solution: Check the recipient's email address for any typos, especially in the domain part. If the address is correct, the recipient's domain may have issues.

550 5.7.1 Unable to relay

  • Meaning: The sender's email server is not authorized to relay messages through the recipient's email server.

  • Solution: Check your email server settings to ensure proper SMTP authentication is configured. You may need to contact your email service provider to enable relaying or to get assistance with configuration.

553 5.1.3 Syntax error in email address

  • Meaning: The recipient's email address is not correctly formatted.

  • Solution: Correct the email address to ensure it follows the standard format (e.g., username@domain.com).

550 5.7.0 Blocked by recipient

  • Meaning: The recipient's email server has blocked the sender's email, possibly due to spam filtering.

  • Solution: Review the email content to ensure it complies with best practices and does not contain spam-like characteristics. Contact the recipient to request unblocking or whitelisting of your email address.

451 4.3.0 Temporary server error

  • Meaning: There is a temporary issue with the recipient's email server.

  • Solution: Try resending the email later. If the issue persists, the recipient should contact their email service provider to resolve the server problem.

554 5.7.1 Message content rejected

  • Meaning: The content of the email was rejected by the recipient's email server, often due to spam or security policies.

  • Solution: Review the email content for anything that might be flagged as inappropriate or spam. Adjust the content and try resending the email.

451 4.7.1 Greylisting in effect

  • Meaning: The recipient's email server is temporarily rejecting the email as part of anti-spam measures.

  • Solution: Your email server will typically retry sending the email after a short delay. If the email is not delivered after multiple attempts, contact your email service provider for assistance.

550 5.2.0 Mailbox disabled

  • Meaning: The recipient's mailbox has been disabled or deactivated.

  • Solution: Contact the recipient through another means to resolve the issue or obtain a new email address.

554 5.3.4 Message size exceeds fixed maximum message size

  • Meaning: The email message is too large to be delivered.

  • Solution: Reduce the size of the email, such as by compressing attachments or sending them through an alternative method, and then resend the email.

452 4.1.1 User over quota

  • Meaning: The recipient's mailbox is full.

  • Solution: The recipient should delete old emails or increase their mailbox quota.

552-5.2.2 The recipient's inbox is out of storage space and inactive

  • Meaning: The recipient's mailbox is not only full but also marked as inactive.

  • Solution: The recipient should contact their email service provider to reactivate the account and clear out old emails.

552 5.1.1 Recipient rejected - extended quota

  • Meaning: The recipient's mailbox has reached an extended quota limit, possibly beyond a temporary increase.

  • Solution: The recipient should permanently increase their mailbox quota or delete unnecessary emails.

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Understanding Bounce Codes

Traditional SMTP bounce codes are three-digit numbers (e.g., 554) which indicate an email’s successful or unsuccessful delivery. If that delivery is unsuccessful, the codes give you insight into why they were unsuccessful.

  • Codes starting with a 4 (e.g., 421) usually indicate a soft bounce.

  • Codes starting with a 5 (e.g., 550) indicate a hard bounce.

Enhanced SMTP bounce codes include three separate digits, separated by periods, which provide more specific details about the mail system error.

  • 2.X.X means successful delivery.

  • 4.X.X means temporary delivery issues (mostly soft bounces).

  • 5.X.X means permanent issues (mostly hard bounces).

The second digit indicates where in the process things went wrong:

  • X.1.X: Addressing issues.

  • X.2.X: Mailbox issues.

  • X.3.X: Mail system issues.

The third digit gives even more detail about the specific issue:

  • 5.1.1: Bad destination mailbox address (e.g., "name" was invalid).

Today, you'll likely see a combination of traditional and enhanced codes. For example, Google uses the traditional three-digit code to give a general overview of the issue and the three-number enhanced code to elaborate.

Email Bounce Codes Glossary

Here’s your guide to some of the most common email bounce codes you may encounter and what they mean.

Soft Bounce Codes (4XX and 4.X.X)

These generally indicate a temporary issue with the recipient’s mail server or mailbox. You can safely try to resend your messages to addresses that give you these bounce codes.

  • 421 4.3.0: Temporary system problem. Try again later.

  • 421 4.4.2: Network connection timed out.

  • 421 4.4.5: Server busy, try again later.

  • 421 4.7.0: Our system has detected an unusual rate of unsolicited mail originating from your IP address.

  • 422 4.2.2: The email account is over quota.

  • 441 4.4.1: Error encountered while communicating with primary target IP address.

  • 450 4.2.1: The user you are trying to contact is receiving mail too quickly.

  • 451 4.3.0: Mail server temporarily rejected message.

  • 451 4.3.0: Multiple destination domains per transaction is unsupported.

  • 451 4.4.2: Timeout - closing connection.

  • 451 4.5.0: SMTP protocol violation.

  • 452 4.2.2: The email account that you tried to reach is over quota.

  • 452 4.5.3: Domain policy size per transaction exceeded.

  • 452 4.5.3: Your message has too many recipients.

  • 454 4.5.0: SMTP protocol violation, no commands allowed to pipeline after STARTTLS.

  • 454 4.7.0: Cannot authenticate due to temporary system problem.

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Hard Bounce Codes (5XX and 5.X.X)

These codes generally indicate a permanent issue with the recipient's email address or server. Remove addresses that give you these codes from your email list immediately.

  • 500 5.0.0: Email address does not exist.

  • 501 5.5.2: Cannot decode response.

  • 501 5.5.4: HELO/EHLO argument is invalid.

  • 502 5.5.1: Too many unrecognized commands, goodbye.

  • 502 5.5.1: Unimplemented command.

  • 503 5.5.1: MAIL first.

  • 503 5.5.1: RCPT first.

  • 503 5.7.0: No identity changes permitted.

  • 504 5.7.4: Unrecognized Authentication Type.

  • 510 5.1.0: Other address status.

  • 511 5.1.1: Bad email address.

  • 513 5.1.3: Bad destination mailbox address syntax.

  • 514 5.1.4: Destination mailbox address ambiguous.

  • 516 5.1.6: Mailbox has moved.

  • 517 5.1.7: Bad sender’s mailbox address syntax.

  • 518 5.1.8: Bad sender’s system address.

  • 521 5.2.1: AOL will not accept deliverability of this message.

  • 530 5.5.1: Authentication Required.

  • 530 5.7.0: Must issue a STARTTLS command first.

  • 535 5.5.4: Optional Argument not permitted for that AUTH mode.

  • 535 5.7.1: Application-specific password required.

  • 541: The message could not be delivered for policy reasons.

  • 542 5.4.2: Bad connection.

  • 543 5.4.3: Routing server failure.

  • 544 5.4.4: Unable to route.

  • 546 5.4.6: Routing loop detected.

  • 547 5.4.7: Delivery time expired.

  • 550 5.1.1: The email account that you tried to reach does not exist.

  • 550 5.1.2: The domain name of the email address seems to be invalid.

  • 550 5.2.1: The email account that you tried to reach is disabled.

  • 550 5.2.1: The user you are trying to contact is receiving mail at a rate that prevents additional messages from being delivered.

  • 550 5.4.5: Daily sending quota exceeded.

  • 550, 5.4.5: Daily SMTP relay limit exceeded for user.

  • 550 5.5.3: Too many recipients attached.

  • 550 5.7.0: Mail relay denied.

  • 550 5.7.0: Mail Sending denied.

  • 550 5.7.1: Email quota exceeded.

  • 550 5.7.1: Invalid credentials for relay.

  • 550 5.7.1: Our system has detected that this message is likely unsolicited mail.

  • 550 5.7.1: The user or domain that you are sending to (or from) has a policy that prohibited the mail that you sent.

  • 550 5.7.1: Unauthenticated email is not accepted from this domain.

  • 550 5.7.26: Unauthenticated email from domain-name is not accepted due to domain's DMARC policy.

  • 550 5.7.26: This message does not have authentication information or fails to pass authentication checks (SPF or DKIM).

  • 550 5.7.26: This message fails to pass SPF checks for an SPF record with a hard fail policy.

  • 551 5.7.1: The message was rejected due to classification as virus, spam, or high bulk ratio.

  • 552 5.2.2: This message is larger than the current system limit.

  • 552 5.2.3: Your message exceeded Google's message size limits.

  • 553 5.1.2: We weren't able to find the recipient domain.

  • 554 5.6.0: Mail message is malformed.

  • 554 5.6.0: Message exceeded 50 hops, this may indicate a mail loop.

  • 554 5.7.0: Too many unauthenticated commands.

  • 554: Email rejected due to security policies

  • 555 5.5.2: Syntax error.

  • 560 5.6.0: Other or undefined media error.

  • 561 5.6.1: Media not supported.

  • 570 5.7.0: Other or undefined security status.

  • 571 5.7.1: Delivery not authorized, message refused.

  • 572 5.7.2: Mailing list expansion prohibited.

  • 573 5.7.3: Security conversion required but not possible.

  • 574 5.7.4: Security features not supported.

  • 575 5.7.5: Cryptographic failure.

  • 576 5.7.6: Cryptographic algorithm not supported.

  • 577 5.7.7: Message integrity failure.

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Conclusion

Understanding and managing bounce rates is crucial for maintaining a positive sender reputation, ensuring email deliverability, and achieving better engagement. Regularly monitoring and addressing bounce messages will help keep your email lists clean and improve overall campaign performance.

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