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Inbound SMTP error codes

Understanding Email Transfer Error Responses

This page lists and tries to explain errors you may have received while attempting to deliver messages to Earthlink's platform.
The SMTP response you received contains a unique code starting with ELNK_.
Find the code below to understand the issue you are experiencing and find remediation tips.

Info

All policies and thresholds listed here are subject to change.

1XX

_101

550 5.7.1 Connection refused

Your sending address is listed on the Vade Threat Network List.
This list contains IP addresses which have been involved in spam, malware and/or phishing campains.

For remediation, you can fill out a request here.

_102

550 5.7.1 Sender blocked error

Your sending address is listed on a Validity Blocklist.
This list contains IP addresses which have been involved in spam, malware and/or phishing campains.

For remediation, you can fill out a request here.

_103

421 4.2.1 Connection deferred

The server is temporarily unavailable.
You may retry delivering the message at a later time.

_105

550 5.7.1 Connection refused

Please check your reverse DNS configuration.

_106

550 5.7.1 Sender blocked error

Your sending address is listed on an Abusix Blocklist.
This list contains IP addresses which have been involved in spam, malware and/or phishing campains.

For remediation, you can fill out a request here.

_107

550 5.7.1 Sender blocked error

Your sending address is listed on an Abusix Blocklist.
This list contains IP addresses which have been involved in spam, malware and/or phishing campains.

For remediation, you can fill out a request here.

_108

550 5.7.1 Connection refused

Please check your FCrDNS configuration.

_110

421 4.2.1 Connection deferred

This error is returned when the sending IP address exceeds the concurrent connections limit.
You may retry delivering the message at a later time.

_130

421 4.2.1 Connection deferred

We protect our users from email threats and doing so, we keep track of volume and quality of the traffic we receive.
Your server is the source of unacceptable messages.
You may retry delivering the message at a later time.

_133

421 4.2.1 Connection deferred

Your server is responsible for targetting invalid recipients.
Make sure your lists' recipient addresses are up to date and unsubscribe any address generating bounces.
You may retry delivering the message at a later time.

_136

421 4.2.1 Connection deferred

Your server is rate-limited due to excessive volume sent.
You may retry delivering the message at a later time.

_139

421 4.2.1 Connection deferred

Your server is rate-limited due to excessive connections received.
You may retry delivering the message at a later time.

_142

421 4.2.1 Connection deferred

Your server is rate-limited due to the amount of targetted recipients.
You may retry delivering the message at a later time.

2XX

_201

550 5.7.1 HELO command rejected

Your server's HELO/EHLO string is unacceptable.

_202

550 5.7.1 HELO command rejected

Your server's HELO/EHLO string is unacceptable.

_203

550 5.7.1 HELO command rejected

Your server's HELO/EHLO string is unacceptable.

_204

550 5.7.1 HELO command rejected

Your server's HELO/EHLO string is unacceptable.

3XX

_301

550 5.7.1 Sender rejected

The sender's address format is invalid.

_303

550 5.7.1 Sender rejected

The sender's address is rejected for policy reasons.
Please verify the domain's DNS configuration.

_304

550 5.7.1 Sender rejected

The sender's address is rejected for policy reasons.

_305

450 4.2.1 Sender temporarily rejected

This error is returned when the sending IP address exceeds the messages per session limit.
You may retry delivering the message at a later time.

_306

550 5.7.1 Sender rejected

The sender's address is rejected for policy reasons.

_307

550 5.7.1 Sender rejected

The sender's address is rejected for policy reasons.

4XX

_402

450 4.2.0 Recipient temporarily unavailable

This mailbox is temporarily unavailable.
You may retry delivering the message at a later time.

550 5.5.1 Recipient rejected

We could not accept your email because the message was sent to a non-existent customer/user.
These errors should be treated as an "unsubscribe" by the sender, if a bulk mailer.

_403

550 5.5.1 Recipient rejected

This mailbox does not exist here.

_404

450 4.2.0 Recipient temporarily unavailable

The recipient's mailbox is temporarily protected.
You may retry delivering the message at a later time.

_405

450 4.2.0 Recipient temporarily rejected

Your message reached the authorized number of recipients per message limit.
Impacted recipients should be accepted on next retries.

Try reducing the number of recipients per message.

_406

550 5.7.1 Recipient address rejected

The recipient's address format is invalid.

5XX

_507

451 4.3.0 Message temporarily rejected

The server is temporarily unavailable.
You may retry delivering the message at a later time.

_510

552 5.3.4 Message size limit exceeded

We currently accept messages of 24MB or smaller.

_512

550 5.7.1 Message rejected

The sender's address is rejected for policy reasons.
Please verify the domain's DNS configuration.

_514

550 5.7.1 Message rejected

The message is rejected for policy reasons.

_515

550 5.7.1 Message rejected per sender's <DMARC|SPF> policy

The message fails authentication mechanisms such as DMARC or SPF.