The recipient address matches multiple mailboxes and the server cannot determine which one to deliver to. This is rare and typically occurs with misconfigured mail routing or directory services.
What Does Error 5.1.4 Mean?
Enhanced status code 5.1.4 indicates the address resolves to multiple possible mailboxes and the server cannot determine the correct one. This is uncommon in modern email systems but can occur in complex enterprise environments with overlapping mail routing rules or directory aliases.
This error typically requires the recipient organization to fix their mail routing configuration. As a sender, there is little you can do except contact the recipient through an alternative channel.
Common Causes
- Address matches multiple mailboxes in the directory
- Overlapping mail routing rules create ambiguity
- Distribution list and individual mailbox name conflict
How to Fix Error 5.1.4
- Contact the recipient through an alternative channel
- Ask the recipient organization to resolve the ambiguity in their mail configuration
- Try a more specific email address if available
Frequently Asked Questions
Bounce code 5.1.4 means the email address you specified matches multiple recipients on the destination system, and the server cannot determine which mailbox to deliver to. This ambiguity prevents delivery because the server will not guess the intended recipient. The address needs to be corrected to uniquely identify a single mailbox before the email can be delivered.
Double-check the recipient's email address for typos, extra characters, or copy-paste errors that may have introduced invisible characters. Contact the recipient to confirm the exact, complete email address. If the address contains common name patterns (like "john@" on a server with multiple Johns), use the full, unique address provided by the organization. This is a permanent error that requires manual correction before resending.
This error occurs when the recipient's mail system finds that the address you specified matches more than one mailbox. Common causes include partial addresses, distribution group name conflicts, alias overlaps in the organization's email directory, or addresses created by copying text that includes hidden formatting characters. The receiving server refuses to guess which recipient you intended, so it rejects the message and asks you to clarify.