501 5.5.4: invalid or empty HELO name
Your client greeted Gmail with an empty or invalid name in its EHLO or HELO command, so Gmail refused it and closed the connection.
- Gmail
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 501 5.5.4
- Provider
- Gmail and Google Workspace
- Temporary or permanent
- PermanentRefused for good: the message comes back to the sender, and resending it gets the same answer.
- Who has to act
- The sender. The fix is on the sending side: your domain, your server or your list.
- What the server says
501 5.5.4 Empty HELO/EHLO argument not allowed, closing connection.
What it means
EHLO and HELO carry the client's name, which RFC 5321 expects to be a fully qualified domain name or, failing that, an address literal: an IP address in square brackets. Gmail refuses a greeting with no name at all, and one whose name it considers invalid. Google documents both wordings and links them to its article on HELO and EHLO errors. Devices and scripts are the usual offenders, sending nothing, a name with spaces or characters that are not allowed, or an IP address without its brackets.
Common causes
- A device or script that sends EHLO with no argument.
- A host name with spaces or characters that are not allowed.
- An IP address given without the square brackets that an address literal needs.
How to fix it
- 01Set the client to greet with its fully qualified host name, ideally the name in its PTR record.
- 02If it has no name, use an address literal such as [192.0.2.1].
- 03Update or reconfigure devices that cannot set a proper greeting, or relay them through a mail server.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
- Gmail SMTP errors and codes (Google Workspace Admin Help)knowledge.workspace.google.com
Related codes
- 503 5.5.1EHLO or HELO missing.Your client started sending mail commands to Gmail without first greeting it with EHLO or HELO, which SMTP requires.
- 501Syntax error in arguments.The command was recognised, but what came with it was malformed, often an address or a host name the server cannot accept.
- 5.5.4Invalid command arguments.A valid SMTP command was sent with an argument the server does not accept, because the value was out of range or named a feature it does not know.
Further reading
All 108 Gmail codesEvery code in the wikiPaste your own bounce