* Describe the bug
Using Google’s SMTP relay results in intermittent email errors. It seems to be related to this Nodemailer bug report.
It’s worth noting that I’m using Google’s SMTP relay in a few other apps (unrelated) and I’m not having problems. Just to say that I understand how to create a separate password (in Google Account 2-Factor Auth section, etc.) so I don’t think the problem is fundamentally with my settings.
* Environment
- NocoBase version: 1.7.15; since at least 1.5 or so
- Database type and version: MariaDB
- OS: Docker within Windows 11
- Deployment Methods: docker compose
* How To Reproduce
As you can see, I’m using SMTP relay with port 587 and “secure” set to false. When the emails are rejected, I’m getting the following message:
{
“code”: “ECONNECTION”,
“response”: “421-4.7.0 Try again later, closing connection. (EHLO)\n421-4.7.0 For more information, go to\n421 4.7.0 About SMTP error messages - Google Workspace Admin Help 3f1490d57ef6-e7f7352f44csm831688276.30 - gsmtp”,
“responseCode”: 421,
“command”: "EHLO"Blockquote
}
Screenshots
Breakdown of the Error Message
"code": "ECONNECTION": This is an error code from the Nodemailer library itself, indicating that the underlying TCP connection failed. In this context, it failed because the remote server deliberately closed it."responseCode": 421: This is a standard SMTP (Simple Mail Transfer Protocol) status code. The 4xx series of codes indicates a temporary failure. The specific meaning of 421 is “Service not available, closing transmission channel.”"response": "421-4.7.0 Try again later, closing connection. (EHLO)": This is the human-readable message from the server.
Try again later: This explicitly tells you it’s a temporary issue and retrying later might succeed.closing connection: The server is actively terminating the session.(EHLO): This is the most critical piece of information! The error occurred during the EHLO command. EHLO is the very first step where the client “greets” or introduces itself to the server. Failing at this stage means the problem is not with the email content, recipient, or sender address, but with the connection behavior itself.
gsmtp: This confirms that you are connected to a Google SMTP server.
The Core Issue
The core problem is that your server/application made too many or too frequent connection requests to the Google SMTP server in a short period, triggering Google’s rate limiting and security policies.
Google’s servers monitor metrics like connection frequency and the number of concurrent connections from a single IP address. When they detect unusual patterns (e.g., a sudden burst of new connections, or connections that are immediately dropped), they temporarily “graylist” the IP and return a 421 error to protect their service from what looks like potential abuse.
