SMTP Error 551: User Not Local

SMTP error 551 indicates that the user is not local to the server and provides a forwarding address. This error occurs when the mail server recognizes that the recipient is not local and suggests an alternative address.

What Does 551 Mean?

The SMTP reply code 551 follows the standard SMTP response format:

• 5 = Permanent failure (permanent negative completion reply)
• 51 = User not local; please try

When you receive a 551 error, it means the mail server cannot deliver to the address you specified, but it provides an alternative forwarding address. You should update your records with the forwarding address.

Error Type

• Type: Permanent failure (hard error)
• Category: User location/forwarding
• Action Required: Update email address with forwarding address

Common Causes

1. User Moved: The user has moved to a different email address
2. Account Migration: The account has been migrated to another server
3. Forwarding Configured: The server has forwarding configured for the user
4. Domain Change: The user's domain has changed
5. Account Transfer: The account has been transferred to another provider
6. Alias Resolution: The address is an alias that points elsewhere

How to Resolve

For Email Senders

1. Update Address: Update the email address with the forwarding address provided
2. Verify Forwarding: Verify that the forwarding address is correct
3. Contact Recipient: Contact the recipient to confirm their new email address
4. Update Records: Update your mailing list with the correct address
5. Remove Old Address: Remove the old address if forwarding is not reliable

For Developers

1. Parse Forwarding Address: Extract the forwarding address from the 551 response
2. Update Database: Update the email address in your database with the forwarding address
3. Handle Gracefully: Handle 551 errors by updating addresses automatically
4. Log Changes: Log address changes for audit purposes
5. Verify Forwarding: Verify forwarding addresses before using them

Related SMTP Errors

• 550 - Mailbox Unavailable (Permanent) - Permanent mailbox errors
• 553 - Mailbox Name Not Allowed - Invalid mailbox name
• 554 - Transaction Failed - Transaction failures

Examples

Example Error Message

551 User not local; please try <[email protected]>

Example with Enhanced Status Code

551 5.1.2 User not local; please try <[email protected]>

Common Scenarios

• Account Migration: "551 User not local; please try [email protected]"
• Domain Change: "551 User moved; please try [email protected]"
• Forwarding: "551 User not local; forwarding to [email protected]"

Best Practices

1. Parse Responses: Always parse 551 responses to extract forwarding addresses
2. Update Addresses: Update email addresses with forwarding addresses
3. Verify Forwarding: Verify forwarding addresses before using them
4. Log Changes: Log all address changes for audit purposes
5. Handle Gracefully: Handle 551 errors gracefully by updating addresses
6. Contact Users: Contact users to confirm forwarding addresses
7. Monitor Success: Monitor delivery success to forwarding addresses
8. Remove Old Addresses: Remove old addresses if forwarding is unreliable