Email Delivery Failure Code Explanations

Category

Failure Type

Block

1. - Spam Complaint
2. - Blacklist
3. - ISP Block
4. - Content Filter
5. - Spam URL
6. - Excess Traffic
7. - Security Violation / Virus
8. - Technical Error Block
9. - List Practices
10. - Authentication
11. - User-Initiated Block

Hard Bounce

1. - Unknown User 
2. - Bad Domain
3. - Address Error
4. - Closed Account

2999 - Other

Soft Bounce

1. - Mailbox Full
2. - Inactive/Disabled Account
3. - Greylist
4. - Server Too Busy

Technical

1. - Data Format Error
2. - Network Error
3. - Other Receiver Error

4006 - Network Configuration

4999 - Other

Invalid

8001-8999. 

Note: A failure code of "0" indicates no failure occurred.

Likely Causes

Suggested Actions

• Receiving server refuses the connection
• Receiving server refuses to accept email during connection and returns it undelivered
• The receiver has your email address on a blacklist
• Spam complaints, bounce rates, and perceived bounce management

Examine the specific Failure Types to determine the likely causes. Based on the cause, perform the following actions:

• Major ISP—Determine the cause, take corrective action, and seek to lift the block.
• Secondary Domain—Determine incidence (percent blocked) and importance of a domain. If incidence and importance are high, contact the system administrator and company management.
• Otherwise—Invalidate records after 3 to 5 attempts with the same result on subsequent mailings. Contact the recipient for a replacement (better) email address or flag for Address Recapture.

Low Engagement—Recipients may not be engaged with you (no/low opens or

clicks). Inactivity directly correlates to complaints.

• Conduct separate reactivation mailings to inactive recipients. Purge non-respondents from your list.
• Review your email sending cadence and reset it to be consistent with customer expectations and recall requirements.

High/Low Frequency—Recipients may be associating your email with spam if you're mailing too frequently or not frequently enough to prompt recall of permission.

Offer choice to recipients on both frequency and content.

Poor Relevance—Recipients may associate your email with spam if not targeted appropriately or if the content is not relevant to their preferences.

Tighten your targeting criteria and associate your content with preferences. Develop feedback mechanisms to confirm relevance.

Likely Causes

Suggested Actions

Weak Branding—Recipients may not realize that the email is from you if your branding is weak.

Use consistent, prominent branding in your From Address, From Name, and Subject Line.

Weak Permission—Recipients may not associate your email with permission granted to you or a third party (list rental, affiliate programs).

• Use more explicit methods to obtain and disclose permission (unchecked box, confirmation notice).
• Investigate permission practices of affiliates.
• Confirm consent before incorporating third-party names into your list.
• Use more explicit methods to obtain and disclose permission (unchecked box, confirmation notice).
• Investigate permission practices of affiliates.
• Confirm consent before incorporating third-party names into your list.
• Make prominent permission statements to remind recipients why they're getting your email.
• Reconfirm permission and/or track other indicators of sustained interest (response, purchase).

Inadequate Complaint

Management—You may not be

unsubscribing recipients who previously complained or addressing the underlying causes of their complaints.

• Immediately unsubscribe recipients who complain that your messages are spam.
• Act on abusive mail and spam forum issues in a timely manner.
• Establish whitelisting and feedback loops with ISPs, if available.
• Monitor the nature of complaints received and investigate recurring problems.

High Spam Complaints—Your email may be generating a high rate of spam complaints.

1001 - Spam Complaint

• Know your data sources. Investigate their compilation and management practices. Confirm consent before incorporating third-party names into your list.
• Immediately unsubscribe recipients who complain that your messages are spam.

Spam Trap Hits—Your email may have been caught in spam traps used to identify spammers.

Blacklist Remediation—Contact the blacklist owner to request removal. This can be difficult and is not always productive.

Before making contact:

Address the underlying causes Determine the incidence (percent blocked)

Inadequate Complaint

Management—You may not be

unsubscribing recipients who previously complained or addressing the underlying causes of their complaints.

• Immediately unsubscribe recipients who complain that your messages are spam.
• Act on abusive mail and spam forum issues in a timely manner.
• Establish whitelisting and feedback loops with ISPs, if available.
• Monitor the nature of complaints received and investigate recurring problems.

Likely Causes

Suggested Actions

High Spam Complaints—Your email may be generating a high rate of spam complaints.

• See 1001 - Spam Complaint for suggested actions.
• Know your data sources. Investigate their compilation and management practices. Confirm consent before incorporating third-party names into your list.
• Immediately unsubscribe recipients who complain that your messages are spam.

Poor List Management—Your email may be generating high failure rates that are associated with spam or poor list management practices.

• See 1009 - List Practices for suggested actions.

Your email may be blocked because of domain-specific policies (no commercial email), resource constraints, etc.

• Contact your ISP for information on their blocking policies.

Your email may have triggered a spam filter due to:

• Prohibited words or phrases
• Too many HTML tags
• Too many images.
• Too many different font styles, sizes, or colors.

• Content Scoring

• Content Review—Based on the content score, reexamine your email templates, adjusting the language, style, and HTML as much as possible without sacrificing effectiveness.

Likely Causes

Suggested Actions

Poor URL Usage—URLs are being used too broadly. The practices of affiliates or others may be impacting your reputation.

• Segregate your URLs. Use distinct URLs for each class of mail (transactional, commercial, newsletter, etc.).
• Verify URL is not being used in other emails perceived as spam (other divisions, affiliates). Investigate the underlying cause of problem URLs.

Low Engagement—Recipients may not be engaged with you (no/low opens or clicks). Inactivity directly correlates to complaints.

• Conduct separate reactivation mailings to inactive recipients. Purge non-respondents from your list.
• Review your email sending cadence and reset it to be consistent with customer expectations and recall requirements.

High/Low Frequency—Recipients may be associating your email with spam if you're mailing too frequently or not frequently enough to prompt recall of permission.

• Review your email sending cadence and reset it to be consistent with customer expectations and recall requirements.
• Offer choice to recipients on both frequency and content.

Poor Relevance—Recipients may associate your email with spam if not targeted appropriately or if the content is not relevant to their preferences.

• Tighten your targeting criteria and associate your content with preferences.
• Develop feedback mechanisms to confirm relevance.

Weak Permission—Recipients may not associate your email with permission granted to you or a third party (list rental, affiliate programs).

• Use more explicit methods to obtain and disclose permission (unchecked box, confirmation notice).
• Investigate permission practices of affiliates.
• Confirm consent before incorporating third-party names into your list.
• Use more explicit methods to obtain and disclose permission (unchecked box, confirmation notice).

Likely Causes

Suggested Actions

• Investigate permission practices of affiliates.
• Confirm consent before incorporating third-party names into your list.
• Make prominent permission statements to remind recipients why they're getting your email.
• Reconfirm permission and/or track other indicators of sustained interest (response, purchase).

Weak Branding—Recipients may not realize that the email is from you if your branding is weak.

• Use consistent, prominent branding in your From Address, From Name, and Subject Line.

Inadequate Complaint

Management—You may not be unsubscribing recipients who previously complained or addressing the underlying causes of their complaints.

• Immediately unsubscribe recipients who complain that your messages are spam.
• Act on abusive mail and spam forum issues in a timely manner.
• Establish whitelisting and feedback loops with ISPs, if available.
• Monitor the nature of complaints received and investigate recurring problems.

Sending Too Much, Too Fast—You may be exceeding the receiving domain's traffic thresholds. Sending too much/too fast is associated with spamming and can result in temporary or permanent blocks.

• Apply domain controls to the receiver mail server (speed throttling, connection limits).
• Retry or resend later and monitor acceptance.

Likely Causes

Suggested Actions

Sender Identity Problem—Your identifying information can't be verified (reverse DNS or valid From and Reply To addresses).

Double-check your DNS entries. Validate your From and Reply To addresses to be sure they actually exist.

Virus Infection—A virus has been detected in your email message or attachment.

Double-check that your mail systems are not infected with viruses or worms. Some may attach themselves maliciously to outbound emails.

Excess Volume—Your cumulative daily volume exceeds
 the number of emails allowed. (Some smaller domains have an inbound volume to protect their servers from Spam.)

Determine incidence (percent block) and importance of a domain. If warranted, spread volume over multiple days.

Likely Causes

Suggested Actions

Stale Data—At 33% address churn per year, your list may contain a high number of undeliverable records if it hasn't been recently mailed or if too much time has elapsed between data capture and mailing.

• While mail frequency should be adjusted for customer preference and value, all segments of your list on a regular basis to ensure brand visibility, continuity of communication and address deliverability.
• Set standards for the first communication after data capture (5 to 10 days). This action will also reduce the likelihood of complaints.
• If mailing to an “old” segment, do a test before full deployment. Deploy the mailing slowly to avoid spikes in Unknown User failures.

Poor Data Capture—You may not be

adequately validating email addresses at the point of data capture.

• Send a follow-up email to new customers to confirm opt-in
 permission and validate the deliverability of the address provided. If the email bounces, invalidate and contact the customer for a new/corrected address.
• Require double entry of email addresses to minimize typographical errors.

Unreliable Data Source—You may be introducing undeliverable records to your list because of unreliable data sources (list rental, affiliate, etc.). A high incidence of stale, inaccurate, or fictitious data suggests a problem.

• Know your data sources. Investigate their data compilation and management practices.
• Confirm consent and deliverability before incorporating third-party names into your list.

Failure to Invalidate—You may not have invalidated previously identified Unknown User failures and removed them from your list.

• Verify that UnknownUser failures have been properly invalidated and removed from your list. If not, immediately do so.

Note: UnknownUser status indicates the email address is valid for the domain but nonexistent. Generally, this means the account has been closed for some time.

UnknownUser failures are associated with spamming (dictionary attacks) and are the most “toxic” type of failure for legitimate mailers. A high incidence typically indicates list management problems.

Likely Causes

Suggested Actions

• Your identifying information cannot be verified via an SPF or Sender-ID record because of a bad record or no record at all.
• Your DomainKeys signature has not been properly configured in your email and DNS servers or is not configured at all.
• If you did not send the message, then someone tried to send an email pretending to be from you and the message was rejected before anyone saw it.

If you are the system administrator for the domain in question, check to make sure that the authentication record for that domain lists the particular server as authorized to send an email on its behalf. If you need help setting up an authentication record, contact support.

Likely Causes

Suggested Actions

Stale Data—Your list may contain “dead domains” if it hasn't been recently mailed.

• If you suppressed a domain due to it being a “dead domain”, upon notification, invalidate records immediately and remove them from your list.

• Contact the recipient for a replacement or corrected email address or flag for Address Recapture.

ISP Block or Other Technical Issues—Your email has been intentionally refused by the receiving ISP or domain, or you are experiencing technical difficulties.

• If you flushed a domain due to blocking issues, determine the cause, take corrective action, and seek to lift the block.
• If you flushed a domain due to an underlying technical problem, determine the cause, take corrective action, and retry or resend and monitor acceptance.

Likely Causes

Suggested Actions

Hard Bounces occur for multiple

reasons, such as address errors, bad domain name names, unknown users, and closed accounts.

Examine the specific Failure Types to determine the likely causes. Based on the cause, perform the following actions:

• Major ISP—Upon notification, invalidate records immediately and remove them from your list. Contact the recipient for a replacement or corrected email address or flag for Address Recapture.

• Secondary Domain—Invalidate records after no more than 2 to 3 attempts with the same result on subsequent mailings. Contact the recipient for a replacement or corrected email address or flag for Address Recapture.

Stale Data—At 33% address churn per year, your list may contain a high number of undeliverable records if it hasn't been recently mailed or if too much time has elapsed between data capture and mailing.

• While mail frequency should be adjusted for customer preference and value, all segments of your list on a regular basis to ensure brand visibility, continuity of communication, and address deliverability.
• Set standards for the first communication after data capture (5 to 10 days) to reduce the likelihood of complaint.
• If mailing to an “old” segment, do a test before full deployment. Deploy the mailing slowly to avoid spikes in Unknown User failures.

Poor Data Capture—You may not be

adequately validating email addresses at the point of data capture.

Send a follow-up email to new customers to confirm opt-in
 permission and validate the deliverability of the address provided. If email

Likely Causes

Suggested Actions

Unreliable Data Source—You may be

introducing undeliverable records to your list because of unreliable data sources (list rental, affiliate, etc.). A high incidence of stale, inaccurate or fictitious data suggests a problem.

• Know your data sources. Investigate their data compilation and management practices. Confirm consent and deliverability before incorporating third-party names into your list.
• Restore Communication—Contact the recipient for a replacement email address or flag for Address Recapture.

Stale Data—Your list may contain “dead domains” if it hasn't been recently mailed.

• While mail frequency should be adjusted for customer preference and value, all segments of your list on a regular basis to ensure brand visibility, continuity of communication and address deliverability.
• If mailing to an “old” segment, do a test before full deployment. Deploy the mailing slowly to avoid spikes in failures.

Poor Data Capture—You may not be

adequately validating email addresses at the point of data capture.

• Send a follow-up email to new customers to confirm opt-in
 permission and validate the deliverability of the address provided. If the email bounces, invalidate and contact the customer for a new/corrected address.
• Require double entry of email addresses to minimize typographical errors.
• Perform Address Correction (hygiene) to correct common misspellings on major domains before adding large quantities of new records to your list. Send confirmation email on corrected records.

Likely Causes

Suggested Actions

Unreliable Data Source—You may be

introducing undeliverable records to your list because of unreliable data sources (list rental, affiliate, etc.). A high incidence of stale, inaccurate or fictitious data suggests a problem.

• Know your data sources. Investigate their data compilation and management practices. Confirm consent and deliverability before incorporating third-party names into your list.
• Restore Communication—Contact the recipient for a replacement email address or flag for Address Recapture.
• Contact the recipient for a replacement or corrected email address or flag for Address Recapture.

Poor Data Capture—You may not be

adequately validating email addresses at the point of data capture.

• Send a follow-up email to new customers to confirm opt-in
 permission and validate the deliverability of the address provided. If the email bounces, invalidate and contact the customer for a new/corrected address.
• Require double entry of email addresses to minimize typographical errors.
• Perform Address Correction (hygiene) to correct common misspellings on major domains before adding large quantities of new records to your list. Send confirmation email on corrected records.

Unreliable Data Source—You may be

introducing undeliverable records to your list because of unreliable data sources (list rental, affiliate, etc.). A high incidence of stale, inaccurate, or fictitious data suggests a problem.

• Know your data sources. Investigate their data compilation and management practices. Confirm consent and deliverability before incorporating third-party names into your list.
• Restore Communication—Contact the recipient for a replacement email address or flag for Address Recapture.

Likely Causes

Suggested Actions

Email Address Change—At 33% address churn per year, closed accounts is a major cause of list attrition.

• Given the rate of address churn, customer reactivation should be a key component of any email communication program.
• Request a second/backup email address or a new/better one as a standard part of your data capture and ongoing communications.
• Contact the recipient for a replacement email address if now closed.
• Flag for Address Recapture (eCOA, email append, etc.). To maximize success, link email addresses to offline data (name, postal).

Stale Data—Your list may contain a high number of closed accounts if it hasn't been recently mailed or if too much time has elapsed between data capture and mailing.

• While mail frequency should be adjusted for customer preference and value, all segments of your list on a regular basis to ensure brand visibility, continuity of communication and address deliverability.
• If mailing to an “old” segment, do a test before full deployment. Deploy the mailing slowly to avoid spikes in failures.

Unreliable Data Source—You may be introducing undeliverable records to your list because of unreliable data sources (list rental, affiliate, etc.). A high incidence of stale, inaccurate, or fictitious data suggests a problem.

• Know your data sources. Investigate their data compilation and management practices. Confirm consent and deliverability before incorporating third-party names into your list.
• Restore Communication—Contact the recipient for a replacement email address or flag for Address Recapture.

Likely Causes

Suggested Actions

Soft Bounces occur for multiple reasons, including mailbox over-limit conditions and inactive accounts.

Examine the specific Failure Types to determine the likely causes. Based on the cause, perform the following actions:

• Resend records that fail for temporary conditions.
• Invalidate records only if the same result is received on subsequent mailings over at least 30 days.
• Contact the recipient for a replacement or corrected email address or flag for Address Recapture.

Likely Causes

Suggested Actions

Temporary Condition—The recipient may have received an unusually high email volume or has not checked his account for a while (vacation, travel).

Resend and monitor acceptance

Infrequent Use—A full mailbox may signify that you're mailing to one of the user's less important email accounts.

Consider Full Mailbox failures as a warning sign. Request a second/backup email address or a new/better one. Attempt contact with the customer through alternate means.

Address Change—The recipient may have abandoned this email address. Watch for it to appear as a Hard

Bounce/Closed in future mailings.

Contact the recipient for a replacement email address if reported as Closed in subsequent mailings. Flag for Address Recapture (eCOA, email append, etc.).

Delinquency or Dispute—The recipient may not have paid the subscription fee or is involved in a dispute with the ISP.

Resend and monitor acceptance

Temporary Condition—The recipient may have received an unusually high email volume or has not checked his account for a while (vacation, travel).

Resend and monitor acceptance

Infrequent Use—A full mailbox may signify that you're mailing to one of the user's less important email accounts.

Consider Full Mailbox failures as a warning sign. Request a second/backup email address or a new/better one. Attempt contact with the customer through alternate means.

Address Change—The recipient may have abandoned this email address. Watch for it to appear as a Hard

Bounce/Closed in future mailings.

Contact the recipient for a replacement email address if reported as Closed in subsequent mailings. Flag for Address Recapture (eCOA, email append, etc.).

Likely Causes

Suggested Actions

Greylisting—This is a technique used by smaller ISPs and corporate domains.

• Resend and monitor acceptance

High Traffic—The receiving mail server is overwhelmed with traffic.

• Apply domain controls to the receiver mail server until traffic subsides (speed throttling, connection limits).
• Retry or resend later and monitor acceptance.

Likely Causes

Suggested Actions

Technical failures occur for multiple reasons, including server down or overload conditions and network or DNS errors.

Examine the specific Failure Types to determine the likely causes. Based on the cause, perform the following actions:

• Resolve underlying technical problem and resend records.
• Invalidate records only if the same result is received on subsequent mailings over at least 30 days.
• Contact the recipient for replacement or corrected email address or flag for Address Recapture.

Lengthy Subject Line—Your Subject Line may violate the receiving domain's length restrictions.

• Shorten the message or, if attachments are included, try removing them. Retry delivery later.

Prohibited Characters—Your message may contain prohibited formatting or characters. Smaller domains may not accept foreign language characters.

• Review From, Subject and message content itself for any unusual formatting or characters, retry delivery.

Invalid Headers—The headers in your mail may be incorrectly formatted.

• Review From, Subject and message content itself for any unusual formatting or characters, retry delivery.

Likely Causes

Suggested Actions

Server Down—The receiving mail server may have gone down or timed out.

Double-check that your Internet connection is working and stable. Retry or resend and monitor acceptance.

Routing Issues.—There may be routing issues between you and the receiving mail server

Double-check that your Internet connection is working and stable. Retry or resend and monitor acceptance.

DNS Error—DNS may not be configured properly on your mail server or in your network.

Make sure you're polling a valid DNS server for domain names. Make sure your mail server can poll receivers' DNS servers.

Internal Network Error—You may be experiencing on-premises network issues.

Check your physical Internet connection to your mail servers. Check to make sure you have enough bandwidth allocated to your server.

External Network Error—Your Internet Service Provider may be experiencing intermittent connectivity issues.

Check your ISP connection. Make sure it's working properly. Check for bandwidth latency issues to the Internet.

Likely Causes

Suggested Actions

Configuration Error—Your network configuration files have not been properly set-up or formatted correctly.

Check configuration files for intended set- up, proper formatting, mistakes, or illegal characters.

Virtual Server Error—There was an misconfiguration in your virtual server configuration files

Check your virtual server(s) configuration to make ensure they have the proper access from your network and intended set-up.

Physical Network Error—There is an issue with the network the system is attached to.

• Check your ISP connection. Make sure it’s working properly.
• Check for bandwidth latency issues to the Internet or your internal systems.

Likely Causes

Suggested Actions

work with the system set-up you have.

Failure

Code

Message

Description

8001

Missing '@'

The email address is missing the @ sign.

8002

';' present

The email address includes a semicolon. Semi-colons are not allowed in email addresses.

8003

Multiple '@'

The email address has multiple @ signs.

8004

Presence of '.' before '@'

The email address has a period right before the @ sign. This format is not supported.

8005

Presence of '.' after '@'

The email address has a period right after the @ sign. This format is not supported.

8006

Presence of consecutive '.'

The email address has consecutive periods, which is an unsupported email address format.

8007

>< not closed

Email addresses may include the < and > signs to indicate a friendly name. This reason indicates that the email address

does not use these symbols appropriately.

8013

INVALID EMAILID FORMAT - '\' Present for TO recipient

The recipient's email address includes a backslash. Backslashes are not allowed.

8015

INVALID EMAILID FORMAT - ' '

Present for TO recipient

The recipient's email address includes a space ( ). Spaces are not allowed.

8998

INVALID EMAILID FORMAT -

Length exceeds 255 characters

for TO recipient

The recipient's email address is too long. Email addresses must be less than or equal to 255 characters.

8999

Other invalid format

The email address is invalid for another reason. Please check the email address format.