Why Are My Emails Bouncing Back? Causes and Fixes

If your emails are bouncing back, the bounce message is your best clue. Most bounces happen for one of a few reasons: the address is wrong, the recipient’s mailbox is full, the receiving server has blocked your message, or your domain’s email settings are incomplete. To fix it, read the reason in the bounce, change the one thing that is wrong, and then send again. This guide explains each cause in plain terms.

What a bounce message means

A bounce is a delivery failure notice. Your mail server sends it back to you when it cannot deliver a message. It usually has a subject line such as “Mail delivery failed” or “Undelivered Mail Returned to Sender”.

Bounce messages include a short code. You do not need to understand all of it, but these two parts help:

• The three-digit code (for example 550 or 451). The first digit tells you the type of problem.
• The enhanced code (for example 5.1.1 or 5.7.1). This gives a more specific reason. Use it before the three-digit code when you can.

The first digit matters most:

• 4xx codes are temporary. The receiving server is busy, the mailbox is full, or it wants you to try again later. These are called soft bounces. The mail server often retries on its own.
• 5xx codes are permanent. The message will not be delivered as it is. These are called hard bounces. Resending the same message without changes will usually fail again.

The reason is in the text of the bounce. Read the full message, not only the subject line. Look for words such as “user unknown”, “mailbox full”, “relaying denied” or “authentication”.

Common causes of bounced emails

This table lists the most common causes, what the bounce usually looks like and whether the problem is temporary or permanent.

The exact wording varies between email providers. Treat the table as a guide, not a complete list.

Fix 1: Check the email address for typos

This is the most common reason for a bounce. A 5.1.1 code means the receiving server does not recognise the address. Often the cause is a small spelling mistake, such as a missing letter or a wrong domain ending.

1. Open the bounce message and find the address it was sent to.
2. Compare it with the address you meant to use, letter by letter.
3. Check the part after the @. Common mistakes include gmial.com instead of gmail.com, or a missing .co.uk.
4. If the address is correct, contact the person by another route and ask if the address still works. People change jobs and close old accounts.
5. Correct the address in your contact list or form, then send again.

Do not resend the same message to the same wrong address. It will bounce again. If the address is wrong, remove it from your mailing list so you do not keep sending to it.

Fix 2: Deal with a full mailbox

A full mailbox is a temporary problem. The recipient has no space left for new messages. Your mail server usually retries for a while before it gives up.

You cannot clear the recipient’s mailbox for them. You can:

• Wait a day or two, then send again.
• Ask the person to clear some space, or to check their storage.
• Use another contact method if the message is urgent.

If the message bounces as full again and again, the address may no longer be used. Treat it like a bad address.

Fix 3: Check your domain’s email authentication

Many bounces and spam problems come from missing email settings. These settings tell receiving servers that your mail really comes from your domain. Three settings do most of the work.

SPF, DKIM and DMARC in plain English

• SPF (Sender Policy Framework) is a DNS record. DNS is the system that connects domain names to servers, and DNS records are the settings you edit for your domain. An SPF record lists the servers that are allowed to send mail for your domain.
• DKIM (DomainKeys Identified Mail) adds a digital signature to each message. The receiving server checks the signature against a key published in your DNS.
• DMARC is a DNS policy. It tells receiving servers what to do with mail that fails SPF or DKIM, and it requires the visible sender address to match the domain that passed those checks.

What to do

1. Find out which service sends your email. This might be your web host, a business email provider, a contact form plugin or an email marketing tool.
2. Ask that provider for the SPF and DKIM details they need. Most providers have a setup guide for their settings.
3. Log in to the place where your domain’s DNS is managed. This is often your domain registrar or your hosting control panel.
4. Add or update the SPF record so it includes every service that sends mail for your domain. Only one SPF record should exist for your domain. If you already have one, edit it rather than adding a second.
5. Turn on DKIM in your email provider’s admin panel, then add the DKIM record it gives you to your DNS.
6. Add a DMARC record if your provider recommends one. Start with a monitoring policy, which takes no action on failing mail, and tighten it later if needed.
7. Wait for DNS changes to spread. This can take a few hours. Then send a test message to an address you own and check the headers.

Google’s official guidance says that all senders should use SPF or DKIM, and that the sending domain should align with at least one of them. Google also recommends using all three, SPF, DKIM and DMARC. For senders of large volumes of mail, the requirements are stricter. Check the current rules for the email provider your readers use before you rely on any single outcome.

If you are not comfortable editing DNS records, ask your web developer or hosting support to check them. Send them the bounce message so they can see the exact code.

Fix 4: Look at the receiving server’s block

Some bounces with a 5.7.1 code mean the receiving server has decided not to accept your message. The reason is not always clear. It might be a spam filter, a poor sending reputation, a missing authentication setting, or a policy rule.

Check these things:

• Authentication. Work through Fix 3 first.
• Content. Messages with many links, large attachments or sales wording may be filtered. Keep business emails plain and relevant.
• Sending volume. Sending many messages at once, or to old lists, can look like spam. Send to people who asked to hear from you.
• Your sending address. A business email from your own domain is generally treated better than a free address that you do not control. For more on this, see Business Email Address: Why It Matters for Your Credibility.

Do not delete the address after a 5.7.1 bounce without checking the reason. The address may be fine. The block may be caused by your settings.

Fix 5: Fix relay denied errors

A “relaying denied” error means your mail server is not allowed to send mail on behalf of that address. This is common when a website sends mail through a server that has not been set up to accept it, for example a contact form or a WordPress site.

Check the sending settings in your website or email tool. You may need to:

• Use the correct SMTP server (the outgoing mail server) and login details from your email provider.
• Use the sending address that belongs to your domain, rather than an unrelated address.
• Turn on authentication for outgoing mail, if your provider asks for it.

For WordPress sites, the sending settings are often handled by an SMTP plugin. For a step-by-step guide, see How to Use SMTP Server to Send WordPress Emails. For a related error message, see Fix the “530 Relaying Not Allowed” email error.

Common mistakes to avoid

• Resending the same message unchanged after a 550. A permanent error will usually happen again.
• Deleting addresses after every bounce. Remove addresses only when the bounce confirms a bad address, such as a 5.1.1 code. For 5.7 codes, fix your setup first.
• Ignoring the enhanced code. The three-digit code is general. The enhanced code tells you more.
• Adding several SPF records. Keep one SPF record per domain and merge the senders into it.
• Asking people to add you to a safe senders list as a fix. This helps for individual contacts, but it does not solve authentication problems for bulk mail.

Quick checklist

1. Read the full bounce message and note the code and the wording.
2. If the address is wrong, correct it or remove it.
3. If the mailbox is full, wait and try again later.
4. If the code is 5.7.x, check SPF, DKIM and DMARC with your email provider.
5. If the message says relay denied, check your SMTP and sending settings.
6. Send a test to an address you control, then check that it arrives.

Next steps

Start with the bounce message you received most recently. Find its code, match it to the table above, and make one change. Then send a test message. If the bounces continue, keep a note of the codes and the email providers involved, and ask your web developer or email provider to check your settings.

If bounces are part of a wider delivery problem, you may also find Email Delivery Failure: 6 Common Causes and Fixes useful. For a broader look at how websites and email are set up, read Choosing web hosting for small businesses.

FAQ

Is a bounced email the same as a spam message?

No. A bounce is a delivery failure notice. The message was not delivered, so it did not reach the inbox or the spam folder. Spam filtering can cause a bounce, but many bounces have other causes, such as a wrong address.

Should I keep trying to send an email that bounced?

Only if the bounce was temporary, such as a full mailbox, and you have waited. If the code is permanent (5xx), correct the cause first. Resending without changes usually fails again.

How do I know if SPF or DKIM is the problem?

Look for a 5.7 code in the bounce, or ask your email provider whether your domain has SPF and DKIM set up. Your provider can usually confirm which records you need and whether they are published correctly.

Can I fix bounces without editing DNS records?

Some causes, such as a typo or a full mailbox, need no DNS changes. Authentication problems usually do. If you are unsure, ask your web developer or hosting support to check the records with you.

Keep Reading

EmailFix “Unable to Verify Account Name or Password” Email ErrorsBusiness TipsEmail Delivery Failure: 6 Common Causes and FixesEmailFix the “530 Relaying Not Allowed” email error