Mdsend

Send markdown files as electronic mail. Maintain mailing lists as templated text files.

Features

• Durable: mail queues are fault tolerant and atomic, brokered by <www.watermill.io> over SQLite3. Can handle any volume of mail without degredation.
• Portable: runs on many kinds of systems. Will include an embeddable HTTP service and Posgres support in the future.
• Flexible: select the mailer backend based on highest deliverability. Swap it out later without changing anything in your letters or templates.
  • Supports recipient list formats: CSV, JSON, YAML, TOML, and Cue.
  • Supports mailing services:
    • SMTP (SMTP_HOST, SMTP_PORT, SMTP_USERNAME, SMTP_PASSWORD)
    • Mailgun (MG_API_KEY, MG_API_DOMAIN) or SMTP relay
    • Resend via SMTP relay or (RESEND_API_KEY)
    • Amazon SES (requires AWS configuration present, beta)
    • SparkPost (alpha)
    • Loops
    • Cloudflare send
  • Supports additional mailing services by SMTP relay:
    • SMTP2GO
    • Brevo
    • Mailchimp
    • Twilio
    • SparkPost
    • Postmark
    • SendGrid
    • ZeptoMail
    • SendPulse
    • MailTrap
    • MailJet
    • EmailLabs
    • PurelyMail
    • HubSpot? (smtp.hubapi.com)

SMTP relay is often more robust than the provider API. For example, Resend API does not support multi-value headers, but its SMTP relay does.

Examples

Compose a letter as a Markdown file. It must include the subject, the sender, and at least one recipient in the frontmatter:

---
subject: "Test Email"
from: "Sender <test@gmail.com>"
to: "Recipient <test@gmail.com>"
---

# Title of the Example Letter

Write text in **Markdown** notation.

Provide server credentials and point mdsend at the saved file.

export SMTP_HOST=...
export SMTP_PORT=...
export SMTP_USERNAME=...
export SMTP_PASSWORD=...
mdsend letter.md

More usage examples are here:

• 1-minimal.md
• 2-attachments.md
• 3-scheduling.md
• 4-themes.md
• 5-templates.md
• 6-list.md
• 7-extending.md

Installation

• MacOS:

  brew tap dkotik/tap
  brew install curl mdsend

• Debian Package: latest release
• Linux Binary: latest release
• Windows Binary: latest release
• Build from source:

  go install github.com/dkotik/mdsend/cmd/mdsend@latest

Development

Mdsend is under active development. Version 1.0.0 is expected by the end of 2026.

This is the list of planned features. ↩

• service package with HTTP unsubscribe endpoint package
• Queue clean up scanner - should be first added to sqlite Watermill driver.
• Sending message with scheduling delay (instead of only queuing) should prompt a confirmation.
• list out templating functions in the example, including the default ones
• Write a better Goldmark 2.0 renderer that recognizes single-line youtube and image paragraphs, centers them.
• Lots of disk usage: each message is pre-rendered plaintext + html and all of that gets duplicated into watermill - i can probably pull out of the main table, but felt like extra read calls; if i add caching can trim that down
• Beautify the default template. Add dark.html one.
• Event invitations markup: https://developers.google.com/gmail/markup/reference/event-reservation#basic_event_reminder_without_a_ticket
• https://github.com/charmbracelet/glamour
• Run some tests with https://www.suped.com/tools/email-tester
• modularize the proprietory mailers - they should not be in default dependencies
• add to https://github.com/rothgar/awesome-tuis and bubbletea list of apps

E-mail Tools

• https://www.caniemail.com/ - check what is template-appropriate
• E-mail message validators:
  • https://www.mail-tester.com/
  • https://www.suped.com/tools/email-tester
  • https://www.htmlemailcheck.com/check/
  • https://github.com/mailhog/MailHog
• Address verification:
  • https://github.com/AfterShip/email-verifier
  • https://github.com/reacherhq/check-if-email-exists
  • https://hunter.io
  • https://verify-email.org
  • https://email-checker.net
  • https://github.com/mailcheck/mailcheck
  • https://github.com/ivolo/disposable-email-domains
  • https://github.com/willwhite/freemail
• Hosting:
  • https://github.com/modoboa/modoboa
• Beautiful templates:
  • https://mjml.io/templates

Similar Projects

• https://github.com/domodwyer/mailyak
• https://github.com/charmbracelet/pop
• https://github.com/wneessen/go-mail
• https://github.com/go-gomail/gomail
• https://github.com/mailhog/mhsendmail
• https://sendune.com/