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Understanding Email Delivery Errors

Below is a comprehensive guide to the most common email error messages and what they mean.

Updated over a week ago

Hard vs. Soft Bounces, Error Codes & What to Do

When sending emails, it’s normal to occasionally run into delivery issues. At Raklet, we help you understand these problems by identifying the type of error and what actions you can take to resolve them (if needed).

In this guide, we’ll break down:

  • The difference between hard and soft bounces

  • What do common email error codes mean

  • How Raklet handles these errors

  • Practical tips for improving your email deliverability

What Are Bounces?

A bounce happens when an email can’t be delivered to the recipient's inbox. The receiving email server usually returns a reason, and based on that, Raklet classifies bounces into two categories:

Hard Bounces = Permanent Failures (Delivery Failed)

These mean the email cannot be delivered permanently, and no retry will be made.

Common reasons:

  • The email address doesn’t exist

  • The domain name is invalid

  • The recipient server has blocked delivery

  • Authentication (SPF/DKIM/DMARC) failed

  • Your domain or IP is blacklisted

Raklet Policy: If an email hard bounces, the address is automatically cleaned from your audience and excluded from future emails.

Note: In rare cases, valid email addresses may hard bounce due to issues on the recipient’s server.

Soft Bounces = Temporary Issues

These are usually caused by short-term problems and may resolve on their own. Raklet will retry sending several times before taking further action.

Common reasons:

  • The recipient’s mailbox is full

  • The server is temporarily down or overloaded

  • Greylisting (temporary deferral)

  • The message size is too large

  • Email blocked due to spam or content filters

  • Temporary domain resolution issues

Raklet Policy:

  • If there is no subscriber activity, we allow 7 soft bounces before converting it to a hard bounce.

  • If the contact has previous activity, we allow up to 15 soft bounces.

Transient (Temporary) Errors

These fall under the "soft bounce" category and usually resolve automatically. Raklet will retry delivery for up to 24 hours.

Error

Description

What You Can Do

Transient-General

Temporary server failure

Wait and let retries run

Transient-MailboxFull

Inbox is full

Try again later or contact recipient

Greylisting / DNS delays

Delayed acceptance of unknown senders

Retry will happen automatically

Permanent (Hard) Errors

These indicate the message cannot be delivered and won't be retried. Raklet marks the address as a hard bounce and removes it from future sends.

Error Code

Description

What You Can Do

550 – Mailbox Unavailable / User Not Found

Invalid or deleted email address

Check for typos or contact recipient

553 – Mailbox Name Not Allowed

Invalid email format

Fix the address format

552 – Exceeded Storage Allocation

Attachment too large or mailbox full

Reduce email size

554 – Transaction Failed

Generic permanent error

Check domain blacklists, spam score, or authentication issues

Authentication-Related Failures

Raklet supports authentication standards like SPF, DKIM, and DMARC to prevent spoofing and improve deliverability.

Failures in these records may result in delivery errors.

Protocol

Purpose

What to Check

SPF

Verifies sending server IPs

Ensure SPF includes your email service

DKIM

Verifies message integrity

Make sure DKIM is properly signed

DMARC

Aligns SPF/DKIM with the sender domain

Use mxtoolbox.com or your DNS provider to check records

Troubleshooting Tips

  • ✅ Test with a plain-text version of your message

  • 🚫 Avoid spammy phrases like “Buy now”, “Free!”, excessive formatting or suspicious links

  • 🔐 Always send from an authenticated domain (with SPF/DKIM/DMARC)

  • 📤 Keep attachments small and relevant

  • 📩 Use a valid reply-to address

  • ❗ Check if your domain or IP is blacklisted

  • 💬 Contact support if you’re repeatedly seeing the same errors

Email Bounce Reporting on Raklet

  • You can view bounce reasons and status for each campaign in your email report dashboard (Details).

  • The receipts for your bounces will be available in your email reports for 30 days after the email is sent.

  • Raklet cannot predict in advance whether a message will bounce — bounces depend on external server rules and recipient configurations.

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