Plunk consolidates transactional emails, marketing campaigns, and drip automation into one platform riding AWS SES at roughly one-tenth of a cent per message, with zero per-contact charges regardless of list size. The Turborepo monorepo architecture separates the Express.js API server (handling REST requests with Prisma ORM against PostgreSQL) from a dedicated BullMQ worker process that consumes email, campaign, and workflow jobs independently for fault isolation and horizontal scaling. Transactional emails support HTML bodies, template variable substitution via React Email components, attachments, and custom headers with dedicated SMTP relay on ports 465 and 587 for integration with existing frameworks. The campaign system sends newsletters and product updates to full contact lists or dynamically segmented audiences based on contact properties and behavioral events, with scheduling, A/B testing, and performance tracking for opens, clicks, and bounces. The workflow automation builder creates event-triggered sequences with delays, conditional branches, and webhook steps for lifecycle campaigns like onboarding drip sequences and re-engagement flows. Contact management stores unlimited contacts with custom data fields, CSV import, full activity history, and dynamic segmentation. Custom domain verification with DKIM and SPF ensures deliverability, while inbound email processing handles incoming messages with custom routing rules. Docker Compose deployment runs five containers including PostgreSQL, Redis, MinIO for S3-compatible storage, and ntfy for notifications. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. AGPL-3.0 licensed.

MillionSend is an open-source email platform you run yourself that sends transactional and marketing mail through your own AWS SES account behind a Resend-compatible API. Every message you send becomes a row in the dashboard, and every row opens into a timeline of SES events with the raw payload and the SMTP diagnostic when something bounces. Daily metrics chart sent, delivered, opened, clicked, bounced, and complained volumes against SES thresholds, and broadcasts stop on their own at five percent bounces or 0.1 percent complaints before Amazon can pause your account. Contacts live once for the whole team with custom properties and subscribe state, while segments and topics decide exactly who receives each broadcast. You compose broadcasts from reusable templates with per-contact merge fields, schedule them ahead, and cancel them while they wait. Applications that only speak SMTP send through the relay on port 2587 with an API key as the password, and HTTP integrations use idempotency keys, request logs with secrets redacted, and signed webhooks with a delivery history. Guided domain setup handles DKIM records, hard bounces and complaints are suppressed automatically, and every recipient gets an RFC 8058 one-click unsubscribe. Receiving and agent-ready inboxes are included in beta for mail sent to your verified domains. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. AGPL-3.0 licensed.

Built as a developer-first alternative to SendGrid, Mailgun, and Postmark, Posta delivers a complete self-hosted email infrastructure platform handling both outbound delivery and inbound reception through a single HTTP API with official SDKs for Go, PHP, and Java. The Go backend processes email through Redis and Asynq with automatic retries, priority queues, and async delivery while PostgreSQL stores templates, contacts, campaigns, and delivery analytics. Outbound features include versioned multi-language templates with variable substitution and stylesheet inlining, bulk campaigns with subscriber targeting and A/B testing per-variant metrics, scheduled timezone-aware delivery with draft/paused/cancelled lifecycle states, email address verification checking syntax, MX records, disposable domains, and role accounts, plus web view links with signed expiring URLs and one-click unsubscribe headers. The built-in SMTP receiver with TLS handles inbound email at your domains, parses messages and attachments, scores spam, and forwards structured payloads to your application via HMAC-verified webhooks with real-time SSE notification streams. The Vue-based dashboard manages templates, SMTP server pools, domains, contacts, API keys, campaigns, and email logs with dark and light mode support while admin-level platform metrics expose delivery rate trends, bounce rate graphs, and latency percentiles alongside Prometheus integration and daily health reports. Deploy via Docker with PostgreSQL and Redis. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. Apache 2.0 licensed.

One notify() call is all your product needs to reach users on push, email, SMS, chat, and webhooks, with NotifKit deciding how and when each message travels. List the channels in the order you prefer and NotifKit tries each in turn, so a failed push quietly becomes an SMS or an email instead of a lost message. Per-user preferences, consent, and quiet hours in each user's own timezone hold non-urgent sends until morning, while critical messages such as one-time passwords travel their own lane immediately. Templates, multi-step workflows that wait days or block on events, scheduling, throttling, and deduplication all run behind that single call, defined in TypeScript and kept in your repository. Delivery logs record every attempt, and the admin dashboard shows a live activity feed, queue depth per priority lane, workflow runs step by step, and a replayable dead-letter queue. Several products can share one deployment as separate projects with their own API keys, rate limits, and data, and any service can call the REST API without the TypeScript SDK. Ask an AI assistant why a password reset never arrived by connecting the built-in MCP server to Claude Code, Cursor, or another MCP client. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. MIT licensed.

Marketing campaigns and transactional mail from one open-source platform: Notifuse is a modern, self-hosted alternative to Mailchimp, Brevo, and Klaviyo without per-email or per-contact pricing. Built with Go and React on PostgreSQL, it separates concerns cleanly: a drag-and-drop visual builder composes responsive templates from MJML components with Liquid variables like {{ contact.first_name }} and per-template version history; campaigns add A/B testing across subject lines, content, and send times; and a REST transactional API serves application-triggered mail. Delivery routes through your choice of provider - Amazon SES, Mailgun, Postmark, SendGrid, SparkPost, Mailjet, or plain SMTP - with multi-provider failover. Contacts carry custom fields and a full activity timeline (messages, profile changes, webhook events), and real-time segmentation builds dynamic rules over properties, activity, and subscriptions. Event-driven automations create behavioral sequences, a notification center gives recipients self-service preference management, and an S3-compatible file manager handles images with CDN delivery. Multi-tenant workspaces with isolated databases and custom domains suit agencies. Open and click tracking report engagement in real time.

Among open-source Mailchimp alternatives, Keila has the most modern UI - built in Germany on Elixir and Phoenix (the PETAL stack), with GDPR-conscious defaults including an optional no-tracking mode, and 100% open source with no proprietary premium tier. Campaign authoring is flexible three ways: a visual block editor with multi-column layouts, Markdown with or without WYSIWYG for hybrid HTML-plus-plain- text sends, and raw MJML for hand-coded designs. The personalization system is unusually clean - every contact carries custom data as a single JSON object (populated from sign-up form fields or pushed from your CMS/CRM), and Shopify's Liquid template language renders it into fully dynamic emails. Targeting uses a visual segment editor backed by a powerful segment language for complex logic over tags, language preferences, and any custom field. Sign-up forms with custom fields grow your lists; open and click tracking measures campaigns; scheduled sending handles timing. Delivery pipes through your own SMTP or first-class integrations with AWS SES (including automated bounce handling), SendGrid, Mailgun, and Postmark. A full REST API manages contacts, campaigns, and segments, with Erlang/OTP reliability underneath. Comfortable at 100K+ subscribers. AGPL-licensed, EU-hosted project, actively developed.

Seven million emails from a single binary peaking at 57 MB of RAM: listmonk is a high-performance newsletter and mailing list manager in Go with PostgreSQL as its only dependency - no Redis, no worker processes, no message broker. The project's own production benchmark sent 7+ million emails with the binary peaking around 57 MB of RAM, and throughput exceeds 100K emails per hour on modest hardware. Campaigns run through a multi-threaded, multi-SMTP queue with round-robin delivery, per-server concurrency, retries, and sliding-window rate limiting across providers like Amazon SES, SendGrid, Mailgun, or your own Postfix relay. Subscribers carry custom JSON attributes and are segmented with raw SQL queries, so any audience Postgres can express, listmonk can target. Templates use Go template syntax with 100+ functions for dynamic per-subscriber content, and the Vue dashboard reports opens, clicks, bounces, and unsubscribes with automated bounce processing. A REST API handles transactional email and programmatic control, a built-in media library hosts campaign assets, and CSV or API import migrates lists from hosted platforms. The economics are the headline: where Mailchimp pricing scales with list size, listmonk plus Amazon SES sends the same volume for hosting cost plus roughly $0.10 per thousand emails - commonly a 95% reduction - and your email list, a core business asset, stays on your own infrastructure. AGPLv3-licensed; bring your own SMTP provider for delivery.

With over 15,000 GitHub stars accumulated since its February 2025 launch, BillionMail delivers the rare combination of a production mail transfer agent and a full email marketing suite in a single self-hosted package — eliminating the monthly per-subscriber fees charged by Mailchimp, SendGrid, and similar platforms. The Go-based architecture bundles Postfix for SMTP transmission, Dovecot for IMAP and POP3 mailbox access, Rspamd for intelligent spam filtering and greylisting, and RoundCube for browser-based webmail, all orchestrated through Docker Compose with PostgreSQL for persistent storage and Redis for queue management and caching. The marketing engine supports unlimited subscriber lists with tag-based segmentation, scheduled campaign sends, A/B subject line testing, and both HTML and drag-and-drop visual template editors for crafting responsive emails without coding. Real-time analytics dashboards track sent volume, deliverability rate, open rate, click-through rate, and bounce reasons, while the platform provides step-by-step DNS record configuration wizards for SPF, DKIM, and DMARC to maximize inbox placement. A transactional email API exposes REST endpoints for single and batch sending, enabling integration with CRM systems, e-commerce platforms, and custom applications. Auto-provisioned free SSL certificates, Fail2ban brute-force protection, and privacy-first architecture with zero third-party tracking ensure secure operation. The platform installs in under eight minutes via a single shell script and supports SMTP on port 25, SMTPS on 465, submission on 587, IMAP on 143/993, and POP3 on 110/995. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. AGPLv3 licensed.

Unlimited agents, unlimited tickets, unlimited mailboxes, forever, on a $4 VPS - FreeScout's pricing inversion is why it became the most popular self-hosted Help Scout alternative, a PHP/Laravel help desk and shared inbox developed from scratch over eight years. The inbox deliberately behaves like Gmail or Outlook, so new support agents need close to zero training. The email-support core is genuinely complete: seamless IMAP/SMTP integration including modern Microsoft Exchange authentication, collision detection that warns when two agents open the same conversation, canned responses, auto-replies, internal notes, open tracking, starring, forwarding, merging, and moving conversations between mailboxes, phone-call logging, push notifications, and an auto-refreshing conversation list - plus screenshot pasting straight from the clipboard into replies. It's 100% mobile-friendly, fully screen-reader accessible, and translated into 28 languages. Beyond the core, an ecosystem of 100+ modules (mostly one-time $12-20 purchases) adds knowledge base, workflows with Gmail-filter-style automation rules, satisfaction ratings, time tracking, tags, custom fields, LDAP, Slack, WhatsApp and Telegram channels, and an API with webhooks - pay only for what your team needs. Web installer and updater included. AGPL-licensed.

A campaign engine wrapped around a contact database: Mautic, the largest open-source marketing automation platform, replaces HubSpot or Marketo without per-contact pricing. Contacts arrive through forms, landing pages, imports, or the REST API and flow into segments: dynamic filters that update automatically from behavior, custom profile fields, or point scores. Segments decide who qualifies; campaigns decide what happens. The drag-and-drop Campaign Builder composes multi-step workflows from actions, positive/negative decision trees, and conditions (field values, tags, device type, segment membership, point thresholds), with static or relative delays, a Jump-to-Step action for moving contacts between branches, and handoffs that push contacts into CRMs or entirely different campaigns. Messaging covers email, SMS, and web/app push out of the box, with A/B testing and a drag-and-drop email builder; dynamic website content swaps page sections per known contact. Lead scoring assigns points for clicks and visits with decay for inactivity, while stages track funnel position. Native integrations cover Salesforce, HubSpot, Zoho, and Dynamics, plus a full REST API for custom sync. It runs on PHP and MySQL with cron jobs processing campaigns and segment rebuilds - self-hosting keeps your entire contact database and behavioral history under your control.

Powering notification delivery for thousands of organizations with over 39,000 GitHub stars, Novu is the open-source communication infrastructure that eliminates the need to build separate integrations for every messaging channel. The TypeScript-based platform provides a single API endpoint that routes notifications across In-App Inbox, Email via SendGrid, Mailgun, AWS SES, and Postmark, SMS through Twilio, Vonage, and Plivo, Push via Firebase Cloud Messaging, Expo, and APNS, and Chat through Slack, Discord, Microsoft Teams, and WhatsApp. The embeddable React Inbox component delivers real-time WebSocket-powered notifications with read/unread states, action buttons, and user-controlled preferences directly inside your application. The workflow engine orchestrates complex multi-channel delivery with conditional branching, time delays, digest batching to reduce notification fatigue, throttle controls, and per-step channel fallbacks. Novu Connect introduces Agent Communication Infrastructure enabling AI agents built with LangChain, Claude, or custom frameworks to hold threaded two-way conversations with humans across any supported channel through a single conversation model with identity resolution and credential management. The backend runs on Node.js with NestJS, MongoDB for notification storage, Redis with BullMQ for job queuing, and Socket.io for real-time delivery. Self-hosting deploys via Docker Compose with the dashboard accessible at port 4200. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. MIT licensed.

With 14,000 GitHub stars and 81 releases since March 2023, Stalwart is the most protocol-complete open-source mail server available — delivering JMAP, IMAP4rev2, IMAP4rev1, POP3, SMTP, CalDAV, CardDAV, and WebDAV from a single Rust binary that compiles to a memory-safe, zero-garbage-collection executable with predictable latency under load. The SMTP server implements DMARC, DKIMv2, DKIMv1, SPF, and ARC for complete message authentication with automatic DKIM key rotation, while transport security enforces DANE, MTA-STS, and SMTP TLS reporting to prevent downgrade attacks. Built-in spam filtering with statistical classifiers, DNS blocklists, and collaborative reputation databases eliminates the need for external Rspamd or SpamAssassin deployments. Encryption at rest protects stored messages with S/MIME or OpenPGP, and automatic TLS certificate provisioning via ACME supports TLS-ALPN-01, DNS-01, and HTTP-01 challenges without manual certificate management. The ManageSieve server enables server-side email filtering rules, while full-text search indexes message bodies and attachments for instant retrieval. Pluggable storage backends support RocksDB for embedded deployments, PostgreSQL, MySQL, and S3-compatible object storage for distributed architectures. LDAP and SQL-based authentication integrate with existing directory services, and the web administration panel manages domains, accounts, quotas, and DKIM keys. Security audited with memory safety guaranteed by Rust's ownership model. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. AGPL-3.0 licensed.