503 5.5.1: EHLO or HELO missing
Your client started sending mail commands to Gmail without first greeting it with EHLO or HELO, which SMTP requires.
- Gmail
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 503 5.5.1
- 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
503 5.5.1 EHLO/HELO first.
What it means
Every SMTP session opens with EHLO or HELO, in which the client names itself. Gmail received MAIL FROM or another command before any greeting, so it refused it and asked for EHLO or HELO first. The same reply can follow STARTTLS: once encryption starts, the session begins again and the client is expected to send EHLO a second time, so clients that skip that step see this. Google links the reply to its article on HELO and EHLO errors. Fix the client; retries fail in the same way.
Common causes
- A client or script that sends MAIL FROM without greeting the server.
- A client that skips the second EHLO after STARTTLS.
- A device with minimal SMTP code.
How to fix it
- 01Make sure the client sends EHLO with its fully qualified host name at the start of every session.
- 02After STARTTLS succeeds, have the client send EHLO again before MAIL FROM.
- 03Update the device or library, or relay it through a mail server that handles SMTP correctly.
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
- 501 5.5.4Invalid 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.
- 503 5.5.1Command sent out of sequence.Your client sent Gmail an SMTP command at the wrong point in the conversation, such as the message before any recipient, so Gmail refused it.
- 503Bad sequence of commands.The client sent a command at the wrong point in the conversation, for example message data before any recipient was accepted, or mail before logging in.
- 5.5.1Invalid SMTP command.The sending software issued an SMTP command that the server does not support, or sent it at the wrong point in the conversation.
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