Built-in SMTP email transport for generic SMTP credentials

[swissky]

Summary

Issue #1541 requests a first-class SMTP email transport in core so operators can send mail through any standard SMTP server instead of only HTTP transactional APIs.

I've implemented this in PR #2156. Opening this Discussion to satisfy the feature-PR requirement for a maintainer-approved Discussion.

What the implementation does

• Built-in email:deliver provider registered when EMAIL_SMTP_* env vars are present
• Works with any standard SMTP server (Brevo relay, Office365, Fastmail, Amazon SES, self-hosted Postfix)
• STARTTLS (587) and implicit TLS (465); port 25 refused (Cloudflare blocks it)
• Runs on Cloudflare Workers (cloudflare:sockets) and Node (node:net/node:tls)
• Env-only config for the first iteration — no admin UI yet

Why it's in core, not a plugin

Sandboxed plugins get exactly one network primitive — ctx.http.fetch() (HTTP/HTTPS only). SMTP is a raw TCP protocol, so a plugin physically cannot open an SMTP connection. Only host code can use cloudflare:sockets / node:net.

Link: #1541
PR: #2156

[marcusbellamyshaw-cell]

thanks