Email verification will not work with email servers that enforce RFC 5321

[mtomasek780]

What happened?

If you are self-hosting and use an email server that enforces RFC 5321 for EHLO messaging being a properly formatted domain, the email cannot be sent. By default, the stoat-api-1 container will send an email with the hostname of the docker container, which is just the container ID. RFC 5321 requires a domain name or IP address, so emails are rejected. Here's a log of the issue occurring from the email server side:

`026-02-22T13:46:09Z TRACE Raw SMTP output sent (smtp.raw-output) listenerId = "smtp", localPort = 25, remoteIp = redacted, remotePort = 57057, size = 43, contents = "220 example.com Lets Talk\r\n"

2026-02-22T13:46:09Z TRACE Raw SMTP input received (smtp.raw-input) listenerId = "smtp", localPort = 25, remoteIp = redacted, remotePort = 47460, size = 19, contents = "EHLO bb5b0be39583\r\n"

2026-02-22T13:46:09Z INFO Invalid EHLO command (smtp.invalid-ehlo) listenerId = "smtp", localPort = 25, remoteIp = redacted, remotePort = 47460, domain = "bb5b0be39583"

2026-02-22T13:46:09Z TRACE Raw SMTP output sent (smtp.raw-output) listenerId = "smtp", localPort = 25, remoteIp = redacted, remotePort = 47460, size = 32, contents = "550 5.5.0 Invalid EHLO domain.\r\n"`

A potential solution is have a variable called domain in [api.smtp] in Revolt.toml or just take the domain from the existing from_address variable. Workarounds can be done by relaying to a server that is more lax in enforcement or using legacy TCP/465 with TLS encryption, but not TCP/587.

[Dadadah]

This is an issue with the stoatchat/stoatchat repository as we are not in control of the configuration. Please open an issue there and link it here in a comment or in your original description.

[mtomasek780]

Thanks, I wasn't quite sure which one to put it in... I did open a ticket there moment ago. I'm not sure what you want to do with this ticket, so I won't close it.

[Dadadah]

Linking ticket: stoatchat/stoatchat#626

[Dadadah]

I'm gonna close this issue. Once it's merged in the backend it'll make it's way to this repo eventually.

[Dadadah]

So I guess I was incorrect here, this can actually be solved by self-hosted. Could you try adding hostname: your.full.domain to your compose.yml for the api server like so:

  # API server
  api:
    image: ghcr.io/stoatchat/api:v0.11.1
    hostname: your.full.domain
    depends_on:
      database:
        condition: service_healthy
      redis:
        condition: service_started
      rabbit:
        condition: service_healthy
    volumes:
      - type: bind
        source: ./Revolt.toml
        target: /Revolt.toml
    restart: always

[Dadadah]

Did more looking into this again. your.full.domain won't work here, as that makes the api server unable to find the other services. Instead, I think in order to use SMTP with restrictive servers you have to create a new subdomain like api.your.full.domain and have it redirect to your.full.domain/api in order to appease the strict domain checking as according to the RFC it is required to resolve to the IP that sent the request.