Common Email Log Error Codes in Salesforce

After every email delivery stage in Salesforce, the recipient mail server sends back a three-digit response code. These codes are found in Salesforce by running an Email Log File. In Salesforce Classic, navigate to Setup > Logs > Email Log Files. In Salesforce Lightning Experience (LEX), navigate to Setup > Environments > Logs > Email Log Files. Download and open the attached log file to verify whether an email was sent and to identify any non-delivery or bounce issues.
Each response code is composed of three digits in the format X.X.X. The first digit indicates the delivery status of the email message:

2 — The email was successfully sent.
4 — There was a temporary problem sending the email. The email server retries automatically, or you must resend it manually depending on your server settings. These errors use codes in the format 4.X.X, where the remaining digits provide more detail.
5 — There is a permanent or fatal error related to the email (for example, the recipient email address does not exist, or the recipient server does not accept emails from your domain). These errors use codes in the format 5.X.X, where the remaining digits provide more detail.

Request an Email Log
Email Log Reference
Mail Non Delivery (NDR) codes

How to Use Salesforce Email Log Error Codes

To troubleshoot email delivery issues in Salesforce, run an Email Log File from Setup > Environments > Logs > Email Log Files and locate the three-digit response code in the downloaded log. Match the code to the descriptions below to understand the root cause and determine next steps.

Common Error Codes in Salesforce Email Logs

The following codes appear most frequently when troubleshooting email delivery in Salesforce:

421 — The mail service is not available and the connection has been closed. The recipient server is temporarily unavailable. Try resending later.
450 — The requested command failed because the user's mailbox was unavailable (for example, the mailbox is full). Try again later.
451 — The command was aborted due to a server error on the recipient's side. This is a transient error; retry delivery.
452 — The command was aborted because the server has insufficient storage. Contact the recipient's mail administrator.
500 — The server could not recognize the command due to a syntax error. Review any custom email headers or configurations.
501 — A syntax error was found in the command arguments.
502 — The command is not implemented on the recipient server.
503 — The server received commands in an incorrect sequence.
504 — A command parameter is not implemented.
550 — The requested command failed because the user's mailbox was not found. The email address does not exist or has been removed.
551 — The recipient is not a local user on the server. Forwarding may be required.
552 — The action was aborted because the recipient's storage allocation was exceeded.
553 — The command was aborted because the mailbox name is invalid. Check the recipient email address format.
554 — The transaction failed for an unspecified reason. Review server logs or contact the recipient's mail administrator.

Full Extended SMTP (ESMTP) Error Code Reference

The following is a complete list of email delivery error codes based on the Extended SMTP (ESMTP) standard. In these codes, X represents either 4 (Persistent Transient error) or 5 (Permanent error), depending on the error type:

X.1.0 — Other address status
X.1.1 — Bad destination mailbox address
X.1.2 — Bad destination system address
X.1.3 — Bad destination mailbox address syntax
X.1.4 — Destination mailbox address ambiguous
X.1.5 — Destination mailbox address valid
X.1.6 — Mailbox has moved
X.1.7 — Bad sender's mailbox address syntax
X.1.8 — Bad sender's system address
X.2.0 — Other or undefined mailbox status
X.2.1 — Mailbox disabled; not accepting messages
X.2.2 — Mailbox full
X.2.3 — Message length exceeds administrative limit
X.2.4 — Mailing list expansion problem
X.3.0 — Other or undefined mail system status
X.3.1 — Mail system full
X.3.2 — System not accepting network messages
X.3.3 — System not capable of selected features
X.3.4 — Message too big for system
X.4.0 — Other or undefined network or routing status
X.4.1 — No answer from host
X.4.2 — Bad connection
X.4.3 — Routing server failure
X.4.4 — Unable to route
X.4.5 — Network congestion
X.4.6 — Routing loop detected
X.4.7 — Delivery time expired
X.5.0 — Other or undefined protocol status
X.5.1 — Invalid command
X.5.2 — Syntax error
X.5.3 — Too many recipients
X.5.4 — Invalid command arguments
X.5.5 — Wrong protocol version
X.6.0 — Other or undefined media error
X.6.1 — Media not supported
X.6.2 — Conversion required and prohibited
X.6.3 — Conversion required but not supported
X.6.4 — Conversion with loss performed
X.6.5 — Conversion failed
X.7.0 — Other or undefined security status
X.7.1 — Delivery not authorized; message refused
X.7.2 — Mailing list expansion prohibited
X.7.3 — Security conversion required but not possible
X.7.4 — Security features not supported
X.7.5 — Cryptographic failure
X.7.6 — Cryptographic algorithm not supported
X.7.7 — Message integrity failure