Feature request: Add Werkmail as an SMTP relay preset

Is your feature request related to a problem?

Option Yes

Describe the solution you'd like

Summary

Please add Werkmail (https://werkmail.eu) to the list of SMTP relay presets in BillionMail's relay setup (Domain → SMTP Relay), alongside the existing AWS SES, SendGrid, and Mailgun options.

Context / why this is scoped as a relay, not a "native provider"

BillionMail is itself a full mail server (Postfix + Dovecot + Rspamd) — it doesn't have a "provider" abstraction the way Notifuse, SendPortal, or listmonk do. The only place an external ESP fits into BillionMail's architecture is as an SMTP relay, used when:

• Port 25 outbound is blocked by the hosting provider (a common cloud VPS restriction BillionMail's own docs call out), or
• A user wants better deliverability/reputation than a cold IP can provide

This is exactly the role AWS SES, SendGrid, and Mailgun already play in BillionMail's relay setup. Werkmail would slot into the same list.

Why Werkmail?

• Fully EU-hosted (Frankfurt / eu-central-1) — relevant for BillionMail users who specifically self-host for EU data residency and would otherwise be relaying through a US-based ESP anyway
• SMTP relay available (in addition to Werkmail's REST API, which isn't relevant here since BillionMail talks SMTP, not APIs, to its relay)
• DSGVO-oriented feature set (consent handling, List-Unsubscribe) complements BillionMail's own DKIM/SPF/DMARC and unsubscribe tooling rather than duplicating it

Suggested implementation

1. Add a "Werkmail" entry to the relay provider dropdown in Domain → SMTP Relay
2. Pre-fill relay host/port/encryption fields (to be confirmed against current Werkmail SMTP documentation — this should be verified before implementation, since Werkmail's most clearly documented integration surface so far is its REST API rather than a published SMTP relay hostname)
3. Standard relay credential fields: username/password (or API-key-as-password, depending on how Werkmail's SMTP auth works)
4. No bounce webhook integration needed here — bounces via SMTP relay are typically returned as standard NDRs, which BillionMail already listens for on port 25

Additional notes

Full documentation:

• https://docs.werkmail.eu

This is a much smaller ask than "native provider" integrations in tools like SendPortal or listmonk, since BillionMail's relay concept is intentionally minimal (host/port/user/pass). Happy to help verify Werkmail's current SMTP relay documentation if that's the blocker.

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Thank you for considering this!

Describe alternatives you've considered

werkmail.eu

Additional

No response