Support optional SMTP\_HELO\_HOST to separate EHLO identity from WEB\_HOST

[S4r4h-O]

Many self-hosted setups serve the web UI on a subdomain (for example, mail.example.com) while sending mail as the root domain (example.com). Today, adjusting that behavior requires a manual code change because the server always uses WEB_HOST (or DOMAIN) for both the UI and SMTP HELO/EHLO.

Suggested Approach
We could introduce a new environment variable, SMTP_HELO_HOST. When set, the server would use it for the HELO/EHLO hostname; otherwise it would fall back to the existing WEB_HOST or DOMAIN.

Details

• Code change in smtp-server.js
  Update the instantiation of SMTPServer so that the name option checks SMTP_HELO_HOST first:

  this.server = new SMTPServer({
  -  name: process.env.WEB_HOST || process.env.DOMAIN,
  +  name: process.env.SMTP_HELO_HOST || process.env.WEB_HOST || process.env.DOMAIN,
     // other options…
  });

• Defaults and documentation
  In .env.defaults, document the new variable:

  # Optional HELO/EHLO hostname. Falls back to WEB_HOST or DOMAIN if unset.
  SMTP_HELO_HOST=

  Add a section to README.md explaining how to:

  1. Serve the UI on mail.example.com while advertising EHLO as example.com (by setting SMTP_HELO_HOST=example.com)
  2. Continue default behavior for single-host setups by leaving it blank

Benefits

• Avoids manual patches for common self-hosted patterns
• Keeps existing behavior unchanged for users who don’t set the new variable
• Improves clarity in configuration and documentation

[titanism]

Can you submit a PR for this?

[S4r4h-O]

Can you submit a PR for this?

I'm not a JS person but I can try