Mailpress

A blog with no admin panel: every post is published by sending an email.

Mailpress is a small, complete Rails 8 application that turns inbound email into blog posts. Send a message to your inbound address and it appears on the site — with the option to keep it as a draft, publish it immediately, or edit an existing post — all driven by the subject line.

How it works

 ┌────────────┐   email.received   ┌──────────────────────────────┐
 │   Author   │ ──── email ──────▶ │  Resend (inbound email)      │
 └────────────┘                    └──────────────┬───────────────┘
                                                  │ webhook (svix signed)
                                                  ▼
                    POST /rails/action_mailbox/resend/inbound_emails
                                                  │
                                        ┌─────────▼─────────┐
                                        │  Action Mailbox   │
                                        │  SenderPolicy     │
                                        │  PostMailbox      │
                                        └─────────┬─────────┘
                                                  │ creates / updates
                                                  ▼
                              ┌───────────┐   ┌───────────────┐
                              │  SQLite   │◀──│  Post (Action │
                              │  (Solid*) │   │  Text + files)│
                              └─────┬─────┘   └───────┬───────┘
                                    │                 │ Turbo broadcast
                                    ▼                 ▼
                              public blog (Hotwire + Tailwind)

1. Resend receives the email and posts an email.received webhook to the app.
2. The official resend gem's Action Mailbox ingress verifies the webhook signature and fetches the full message from Resend.
3. PostMailbox checks the sender against an allowlist, parses the subject, and creates or updates a Post — sanitizing the HTML body and attaching images.
4. Published posts are broadcast over Turbo Streams, so open browser tabs update live. The author gets a confirmation email back through the Resend API.

Email conventions

The subject line is the command. RE: / FW: prefixes are ignored, so you can simply reply to your own confirmation emails.

Subject	Result
PUBLISH: My new post	Creates a published post
DRAFT: My new post	Creates a draft
My new post	Also creates a draft
EDIT: my-new-post	Replaces that post's body with this email's body
EDIT: my-new-post | New title	Replaces the body and renames the post

The email's HTML part becomes the post body (sanitized to a safe allowlist), falling back to the text part rendered as paragraphs. Image attachments are stored with Active Storage and shown under the post.

Stack

• Rails 8.1 — Solid Queue, Solid Cache, Solid Cable, Propshaft, Thruster
• SQLite for the primary, queue and cache databases
• Action Mailbox for inbound email, Action Mailer for outbound
• Resend as the inbound ingress and outbound delivery method
• Hotwire (Turbo + Stimulus) and Tailwind CSS 4
• Minitest, RuboCop, Brakeman and bundler-audit wired into CI

Getting started

Requirements: Ruby 4.0+, SQLite 3.

bin/setup          # install gems, prepare databases, seed demo posts
bin/dev            # http://localhost:3000 (Rails + Tailwind watcher)

Run the test suite and linters:

bin/rails test
bin/rubocop
bin/brakeman
bin/bundler-audit

Configuring inbound email (Resend)

1. Create a Resend account and verify a domain you want to publish from.

2. Enable inbound email for that domain and add an address such as [email protected]. Point the domain's MX records where Resend asks.

3. Create a webhook subscribed to the email.received event targeting:

   https://your-host/rails/action_mailbox/resend/inbound_emails
   

4. Copy the webhook's signing secret (whsec_...) and your API key (re_...) into the environment.

Configuration

Copy .env.example to .env and fill it in:

Variable	Purpose
RESEND_API_KEY	Sends confirmations and fetches full inbound messages
RESEND_INGRESS_SIGNING_SECRET	svix signing secret used to verify webhooks (whsec_...)
MAILPRESS_ALLOWED_SENDERS	Comma-separated allowlist; supports *@domain.com. Empty in dev = allow all
MAILPRESS_MAIL_FROM	From address for confirmation/bounce mail (verified Resend domain)
MAILPRESS_HOST	Public host used in email links (production)

In production, set the same variables (for example with Kamal and .kamal/secrets). Solid Queue processes jobs via bin/jobs.

Testing email locally

Action Mailbox ships a developer conductor at http://localhost:3000/rails/conductor/action_mailbox/inbound_emails where you can paste a raw RFC822 message. You can also drive the whole pipeline from a console:

bin/rails runner '
  raw = "From: [email protected]\nTo: [email protected]\nSubject: PUBLISH: Hi from the console\n\n<p>Hello</p>\n"
  inbound = ActionMailbox::InboundEmail.create_and_extract_message_id!(raw)
  ApplicationMailbox.route(inbound)
'

Without an allowlist configured, development accepts email from any sender so you can try things out before setting up a domain.

License

Released under the MIT License.