Creating and managing app emails can be a tricky business. We’ve developed a number of free services and open source tools that make working with email more enjoyable.
A free tool to monitor & implement DMARC.
dmarc.postmarkapp.com
Instantly check the spam score of your email messages.
spamcheck.postmarkapp.com
A Slack App to receive Bounce notifications and other information from Postmark
postmarkapp.com/slack-app
A nifty integration that lets your customers know about delivery issues straight from your web app.
postmarkapp.com/rebound
A collection of SMTP error codes from major inbox providers.
smtpfieldmanual.com
Agent Skills for the Postmark email platform. Teach AI coding agents how to send transactional email, process inbound messages, manage templates, and configure webhooks using the Postmark API.
github.com/ActiveCampaign/postmark-skills
Integrate Claude and Cursor AI with Postmark to send emails and monitor delivery stats.
github.com/ActiveCampaign/postmark-mcp
Push and pull templates, send emails, and fetch server lists from the command line.
github.com/activecampaign/postmark-cli
A complete toolset to streamline building and updating a set of consistent transactional emails.
postmarkapp.com/mailmason
MailBrush lets you add syntax highlighting to code snippets so they can be used in your email templates.
github.com/activecampaign/mailbrush
Simple lightweight mail library which allows you to send and retrieve emails, and get more details about email sending and delivery.
github.com/activecampaign/mailhandler
Rock-solid email templates for applications.
postmarkapp.com/transactional-email-templates
Simple CSS inlining, for email, for C# and other .net-based languages.
github.com/activecampaign/style-merge
A Lightweight, powerful, flavorful, templating engine for C# and other .net-based languages.
github.com/activecampaign/mustachio
Lightweight quickstart app for receiving and processing webhooks from Postmark.
github.com/activecampaign/postmark_webhooks/
Starter workflow for creating self-signed PDF agreements with node.js and express.
github.com/activecampaign/PactMaker
