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.

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.

Larasend gives Laravel teams a self-hosted transactional email platform that sends through their own Amazon SES or Cloudflare account while keeping the dashboard, delivery logs, and message data on their own servers. Send mail with a simple POST to the emails API, or point existing mailables and notifications at the Larasend transport with one environment variable and no code rewrite. Every message lands in an activity dashboard where you can filter by status, search recipients and message IDs, open a preview with headers and metrics, and resend failures in one click. Delivery, bounce, complaint, open, and click events stream back from the provider and update each message timeline, so a missing receipt becomes a traceable record instead of a support mystery. Suppression lists build themselves from bounces and complaints, and guardrails watch complaint rates and verified domains before reputation damage can spread. Scoped API keys with expiration and rotation keep each project separate, while workspace roles control who can view, send, and administer. When replies arrive, the shared inbox threads inbound and outbound mail into conversations your team can assign, snooze, annotate, and answer with attachments and drafts. Webhooks notify your other systems about deliveries and inbound mail, and reusable templates keep recurring notices consistent across projects. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. MIT licensed.

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.

Product teams get a visual home for the transactional and lifecycle emails their application sends with Senlo, which sits on top of the delivery provider they already use instead of replacing it. A drag-and-drop editor builds responsive templates without hand-written HTML, exports to MJML or plain HTML when needed, and keeps templates versioned so edits can be reviewed and rolled back safely. Event-triggered automations turn product activity into onboarding sequences, trial reminders, and win-back flows: your app feeds contact events through the API, and Senlo decides which message goes out next. The transactional API sends a rendered template in one call, so receipts, password resets, and alerts stop living as scattered strings in your codebase. Delivery stops being a black box, with sends, deliveries, bounces, and engagement tracked per workspace, a live feed of failures, and suppressions that block bad addresses before they damage sender reputation. Because sending stays with Resend, Postmark, SES, Mailgun, or your own SMTP server, switching providers never means rebuilding a template. 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.

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.

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.

With over 7,100 GitHub stars and 200 contributors since 2016, Mailu has become one of the most popular self-hosted email solutions, delivering a complete production-ready mail server stack as pre-configured Docker containers that eliminate weeks of manual setup. The platform bundles Postfix for SMTP and Submission with auto-configuration profiles for Thunderbird, Outlook, and mobile clients, Dovecot for IMAP and POP3 with full-text search across email attachments, Rspamd for intelligent spam filtering with auto-learn Bayesian classification, greylisting, SPF and DMARC validation, and ClamAV for antivirus scanning of attachments with configurable malicious file blocking. The web administration interface provides global admin controls, per-domain delegation, user quota management, domain aliases, custom routing rules, and announcement capabilities. Users access self-service features including aliases, auto-reply, auto-forward, fetched accounts from external mailboxes via fetchmail, and Sieve filter management through ManageSieve. Security features include enforced TLS on all connections, automatic Let's Encrypt certificate provisioning, outgoing DKIM signing, DANE and MTA-STS support for transport security, and Snuffleupagus PHP hardening for the web interface. The setup wizard at setup.mailu.io generates complete Docker Compose configurations tailored to specific deployment requirements. All components are free and open-source software with zero proprietary dependencies and no tracking. 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 over 13,000 GitHub stars and active monthly releases, Mailcow delivers a production-ready mail server infrastructure through Docker Compose orchestration of twelve integrated containers. The stack pairs Postfix as the MTA handling SMTP traffic with Dovecot for IMAP and POP3 retrieval featuring the Flatcurve full-text search engine, while Rspamd provides machine-learning-powered spam filtering with Bayesian classification, DKIM signing, and ARC support. ClamAV scans attachments for malware including Office document macro analysis via Olefy, and SOGo serves as a responsive webmail client with CalDAV, CardDAV, and Microsoft ActiveSync synchronization. The admin panel manages multiple domains, per-user spam score thresholds, quarantine review, black and whitelists, temporary spam aliases, mailbox quotas, and TLS enforcement policies for both inbound and outbound messages. Security features include two-factor authentication via TOTP, WebAuthn, and Yubikey OTP, a Fail2ban-like Netfilter integration for brute-force protection, and automatic SPF, DKIM, and DMARC configuration. The ACME container handles Let's Encrypt certificate generation with DNS-01 challenge support, while Postfix TLS-Pol provides MTA-STS and DANE/TLSA resolution for encrypted transport. Built-in imapsync enables periodic migration from remote mailboxes, and the REST API allows programmatic management of all server resources. MariaDB stores user data, Redis caches configuration and sessions, and Unbound provides local DNSSEC-validating DNS resolution. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. GPL-3.0 licensed.

Stalwart replaces the traditional Postfix + Dovecot + SpamAssassin + calendar-server stack with one Rust binary that speaks every standard mail and collaboration protocol natively. JMAP, IMAP4rev2, POP3, SMTP, CalDAV, CardDAV, and WebDAV all run inside the same process — no glue scripts, no sidecar daemons, no version conflicts between components. The pluggable storage architecture lets operators choose RocksDB for single-node deployments, FoundationDB for distributed clusters, PostgreSQL, MySQL/MariaDB, or SQLite for the data store, S3/MinIO/Azure Blob for message blobs, and Elasticsearch or Meilisearch for full-text search, with Redis or the internal engine backing rate limiters and session state. Security features include S/MIME and OpenPGP encryption at rest, automated DKIM key generation with DNS publication, DANE and MTA-STS transport security, automatic ACME TLS provisioning, granular ACLs, rate limiting, and IP banning. The browser-based admin console manages accounts, domains, groups, mailing lists, SMTP queues, DMARC/TLS-RPT/ARF reports, and every configuration object without touching a config file, while the self-service portal at /account gives end users password reset and encryption key management. Multi-tenant support with per-tenant quotas enables hosting-platform deployments, and coordinator-less clustering via Zenoh or NATS scales horizontally by adding nodes. Deploy via Docker or the standalone binary. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. AGPL v3 licensed.

Modoboa turns a bare mail server into a managed hosting platform, with one web console for domains, mailboxes, aliases, and quotas, plus a full webmail for the people using them. Roles separate super administrators, resellers, domain administrators, and ordinary users, with caps on how many mailboxes and aliases each administrator may create and daily sending limits per domain or mailbox. The webmail offers conversation view, folder subscriptions, scheduled sending, attachments, and search across headers and message bodies. Calendars and address books sync with standard clients, and calendars can be shared. Each user writes Sieve filters and autoreplies in the browser. Deliverability checks cover MX records and DNSBL listings, DKIM keys are generated per domain, and DMARC aggregate reports become per-domain visual reports. Amavis quarantine pages and an Rspamd frontend help with spam. Traffic graphs show message volume. Accounts authenticate against the local database, LDAP, Active Directory, or an existing SMTP server, with TOTP codes or WebAuthn security keys as a second factor. Thunderbird and Outlook configure themselves through built-in autoconfig and autodiscover endpoints. An IMAP migration tool pulls mailboxes from another provider as each person signs in. Administrators can brand the console with custom logos, extend it through plugins, and automate it through a documented REST API. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. ISC licensed.

Running a proper mail server used to mean stitching together half a dozen daemons; maddy folds the whole stack into one binary with one configuration file. It receives mail as your MX, sends as your MTA, stores messages for IMAP clients, and signs and verifies with DKIM, SPF, DMARC, DANE, and MTA-STS so other servers actually trust what you send. The design is composable: checks, modifiers, tables, and delivery targets snap together in the config, so spam scoring, address rewriting, and routing rules read like a pipeline instead of a pile of interlocking config files. Outbound mail queues with retries and backoff, inbound delivery lands in IMAP storage backed by SQLite or PostgreSQL, and a built-in ACME client keeps TLS certificates renewed, including DNS-01 providers. Milter support lets existing filters join the pipeline, authentication spans SASL mechanisms and Dovecot delegation, and Prometheus metrics watch queue length and delivery health from your usual dashboards. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. GPL-3.0 licensed.

Parse DMARC reads the DMARC aggregate reports that Google, Microsoft, and Yahoo email about your domain every day and shows you, in one dashboard, who is sending mail as you and whether it passes authentication. It fetches the reports over IMAP, unpacks the gzip, zip, and XML attachments automatically, and charts your pass rate, message volume, and top sending sources at a glance. Any report opens down to its raw records, so when an unfamiliar IP starts sending as you, the evidence is one click away instead of buried in XML. Reports forwarded through Exchange or Outlook as message attachments are unwrapped too, and a local Maildir intake covers servers where the mailbox lives on the same host. A built-in generator writes your _dmarc TXT record from a form, so tightening your policy does not mean hand-writing DNS syntax from memory. Twenty-eight Prometheus metrics and a shipped Grafana dashboard move the same data into the monitoring stack you already run. An MCP server lets an AI assistant query your reports directly, asking which sources failed DKIM this week in plain language. Everything stores in a single SQLite file inside one static Go binary, with dark mode for late-night incident reviews. 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.

Every email your app sends while you build and test it lands in OwlMail's browser inbox instead of a customer's mailbox. Point any application's SMTP settings at OwlMail and every message is ready to open as rendered HTML, plain text, headers, or raw source. Attachments and inline images sit beside the body, and seven preset preview widths show how the message lays out on phones, tablets, and desktops before anyone real sees it. A Verify panel checks subject, body, and link hosts against expectations, while CI pipelines use the REST API with delivery cursors to wait for exactly the messages their test run produced, assert on them, and clean up afterwards. Coding agents get the same inbox read-only over MCP, so an assistant can confirm a signup email arrived without touching your mail server. When a message proves itself, relay it onwards to a real SMTP server, by hand or automatically under filtering rules, or fire webhooks with HMAC signatures and retry queues into the rest of your automation. Everything stores as plain .eml files on disk, with optional SQLite indexing, S3 attachment storage, and ZIP exports for archiving. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. MIT licensed.