Google SMTP returning intermittent 421 4.7.0 errors

[S1m]

Context:

• Self-hosted on EC2
• Docker compose deployment

SMTP setup was completed using Google smtp-relay. Test emails were succesfully sent.

However, when adding new users, intermittently Google would close the connection prior to HELO with a 421 4.7.0 code. Therefore, these emails were never sent. Users couldn't log in.

Upon investigation:
Nodemailer uses os.hostname() for the SMTP EHLO greeting. In Docker containers, this returns the container ID (e.g., e508959023b2) instead of a valid FQDN. Google's SMTP relay rejects non-FQDN hostnames in EHLO, but inconsistently - causing intermittent failures.
Workaround:
Set hostname: your.domain.com in Docker Compose for the Rocket.Chat container.
Suggested Fix:
Expose nodemailer's name option in Rocket.Chat's SMTP settings (Admin → Email → SMTP). This option sets the EHLO hostname explicitly, independent of the container's system hostname.
References:
Nodemailer name option: https://nodemailer.com/smtp/ ("optional hostname of the client, used for identifying to the server")
Similar issue in other frameworks: loco-rs/loco#1055

[hamzanazir27]

Hi @S1m,

I’ve analyzed the issue. The intermittent 421 4.7.0 error is clearly a result of Google's SMTP relay rejecting the non-FQDN hostnames (container IDs) provided by Nodemailer's default os.hostname() behavior.

While setting the hostname in docker-compose works as a workaround, exposing the name option in the SMTP Settings (Admin → Email → SMTP) is a much more robust and standard fix for the Rocket.Chat ecosystem.

I am a Computer Science graduate and currently working as a MERN Stack developer. I have experience with Nodemailer and Dockerized deployments, and I'd like to work on this.

My proposed plan:

Add a new setting field (e.g., SMTP_Name) in the Email settings schema.

Pass this value to the Nodemailer transport configuration in the backend email service.

Update the Admin UI to include this optional field.

I’m ready to submit a PR for this. Could you please assign this to me or let me know if there are any specific guidelines for adding new SMTP settings?

[Anas-Blue]

Hi!
This PR fixes the Google SMTP 421 issue by making the EHLO hostname configurable via SMTP_Client_Name for all outgoing emails.

Thanks!