MimeKit is a mature, high-performance .NET library for creating, parsing, and manipulating MIME messages (email). It provides comprehensive support for all standard MIME structures (multipart, message/rfc822, content-transfer encodings), internationalized headers (RFC 2047/2231), and email security features including S/MIME, OpenPGP, DKIM, and ARC signing/verification. The library also includes a full HTML5 tokenizer, TNEF (Outlook Transport Neutral Encapsulation Format) reader, text format converters (HTML, flowed, plain), and a stream filter pipeline for encoding/decoding and line-ending normalization. The codebase is well-architected with clean abstractions (visitor pattern, filter chain, encoder/decoder interfaces), extensive unit tests, and benchmarks demonstrating 25x–75x faster parsing than competing .NET MIME libraries. It is distributed as NuGet packages (MimeKit, MimeKitLite) and is a .NET Foundation project. The repository also includes sample applications for Windows Forms, iOS, and Android, and a DKIM verifier sample.
Prometheus Alertmanager is a production-grade Go service that receives alert notifications from Prometheus or any HTTP client, deduplicates and groups them by routing rules, applies silences and inhibition rules, and dispatches notifications through 20+ integrations (Slack, PagerDuty, email, webhook, Telegram, Jira, etc.). It runs as a single binary with an embedded web UI, a REST API v2, an experimental Connect/gRPC API, and an amtool CLI. The architecture is a modular monolith: the app package wires together config loading, cluster membership, HTTP listeners, and a pipeline of notification stages (mute, dedup, retry, fanout).
MailChecker is a cross-platform library for determining whether an email address is from a disposable or temporary email provider. It is implemented in 10+ languages (Node.js, PHP, Python, Ruby, Rust, Go, Java, Elixir, Clojure, etc.) via a centralized template-based code generation system. The library's core is a curated blacklist of over 55,000 disposable email domains stored in a plain text file (`list.txt`). Each platform provides a tiny API: `isValid(email)` returns `true` if the email format is valid AND its domain is not in the blacklist, and `blacklist()` to retrieve the domain list. The code generation pipeline (`lib/generator.js`) uses Mustache templates (`*.tmpl.*`) to produce optimized platform-specific code. The repository also includes domain cleanup scripts and comprehensive per-platform tests run in Docker containers. This is a purely application-oriented library; it does not contain data pipelines, ML models, or research artifacts.
django-anymail is a Django library that provides a unified interface for sending transactional email through multiple Email Service Providers (ESPs) such as Amazon SES, Mailgun, SendGrid, Postmark, SparkPost, Mailjet, Brevo, Resend, Mailtrap, Postal, Scaleway, Unisender Go, and MailerSend. It extends Django's built-in email framework with ESP-specific features like tags, metadata, inline images, merge data, templates, and click/open tracking. The library also handles inbound email and tracking webhooks, normalizing ESP-specific events into Django signals. Architecture follows a backend pattern: each ESP has a concrete EmailBackend class that implements `build_message_payload` and `post_to_esp`, with common logic in base classes (`AnymailRequestsBackend`, `BasePayload`). Webhook views are similarly structured with base classes for signature validation and event dispatch. The codebase is well-tested with both mock unit tests and live integration tests run weekly against real ESP APIs. It is a mature, actively maintained library with a clean separation of concerns and extensive documentation.
MRML is a Rust-based implementation of the MJML (Mailjet Markup Language) parser and renderer. It provides a core library for converting MJML templates to responsive HTML email, along with CLI, WebAssembly, and Python bindings. The architecture is modular, with each MJML component following a consistent pattern for parsing, rendering, and serialization. The system supports template inclusion via pluggable loaders (memory, local, HTTP) and includes an HTTP server example for rendering MJML via a POST endpoint.
Reacher is an open-source email verification system written in Rust. It checks if an email address exists without sending any email by performing syntax validation, MX record lookup, SMTP connection with intelligent response parsing, and miscellaneous checks (disposable, role-based, gravatar, haveibeenpwned). The system is structured as a Rust workspace with four crates: a core library (`check-if-email-exists`), a CLI binary, an HTTP backend server (`reacher_backend`), and an AWS SQS Lambda worker. The backend provides REST API endpoints for single and bulk email verification, supports queue-based scaling via RabbitMQ, and stores results in PostgreSQL. It features a flexible verification method configuration allowing per-provider overrides (Gmail, Hotmail, Yahoo, etc.) with SMTP, headless browser, or API methods, and supports SOCKS5 proxies with routing rules. The codebase demonstrates strong Rust craftsmanship with clean abstractions, builder patterns, comprehensive error handling, and thorough testing.
Bamboo is a mature, well-architected Elixir library for composing and delivering emails through adapters. It provides a clean functional API for building email structs, a powerful address normalization system via the `Bamboo.Formatter` protocol, and built-in adapters for Mailgun, Mandrill, SendGrid, local in-memory storage, and testing. The library supports background delivery, email interceptors, attachments, plug-based preview of sent emails, and comprehensive test helpers. Production code is separated from optional Phoenix view integration (extracted to bamboo_phoenix). The architecture uses behaviours for adapters and delivery strategies, making it extensible. It is actively maintained, with recent commits and CI passing on Elixir 1.17-1.19.
A simple yet rigorously correct .NET library for validating email addresses according to RFC 5322 and Internationalized Email standards (RFC 653x). The core is a hand-written character-by-character parser that rejects invalid syntax while supporting quoted strings, IP literals, international characters, and length constraints per the spec. It provides a static `Validate`/`TryValidate` method and a DataAnnotations `EmailAttribute` for easy integration into ASP.NET or other validation frameworks. The library is well-tested with hundreds of valid and invalid examples, including edge cases like surrogate pairs and maximum-length addresses. It targets multiple .NET frameworks (net462, net8.0, net10.0, netstandard2.0/2.1) and is distributed as a NuGet package with signed assemblies. The code is clean, well-commented, and free of external dependencies for the core validation, making it a trustworthy component for any .NET application needing email input validation.
chasquid is a production-grade SMTP (email) server written in Go, focusing on simplicity, security, and ease of operation. It handles incoming and outgoing email with full support for modern email security standards including STARTTLS, DKIM signing and verification, SPF checking, MTA-STS enforcement, and per-domain security level tracking. The server architecture is modular: the main daemon delegates SMTP protocol handling to the internal/smtpsrv package, manages a persistent email queue via internal/queue, performs alias resolution with hooks via internal/aliases, and delivers mail either locally through an LMTP-based MDA (cmd/mda-lmtp) or remotely via SMTP courier with TLS and MX fallback. Authentication integrates with Dovecot or a local user database using scrypt password hashing. Configuration is defined via protobuf text format, supporting hot reload of domains, users, and aliases without restart. The repository includes CLI tools for administration (chasquid-util), SMTP connectivity checking (smtp-check), and Dovecot authentication testing (dovecot-auth-cli). A comprehensive test suite covers unit, integration, and fuzz tests, with test data for DKIM, SPF, aliases, and various protocol edge cases. The repository also provides a Dockerfile for containerized deployment and extensive documentation in Markdown and man pages. While primarily an application, the codebase contains several well-designed internal packages that could be extracted for reuse, such as the network tracing library, safe I/O utilities, and OpenMetrics exporter.
EmailAnalyzer is a command-line application for analyzing suspicious email files (.eml). It extracts headers, links, attachments, digests (hashes), and authentication results (SPF/DKIM/DMARC) from email messages. The tool provides investigation features that generate links to threat intelligence services (VirusTotal, AbuseIPDB, URLScan) for indicators of compromise found in emails. Output can be displayed in the terminal or saved as JSON or HTML reports. The architecture is modular with separate functions for each analysis component, all depending only on the Python standard library, making them highly reusable.
Novu is a comprehensive notification infrastructure platform designed for multi-channel delivery (Email, SMS, Push, Chat, In-App) and workflow orchestration. It functions as both a SaaS product and a self-hosted solution, providing a unified API to manage subscribers, triggers, and notification templates. The system integrates deeply with AI agents, supporting Model Context Protocol (MCP) and managed runtimes (e.g., Anthropic) for conversational notifications. The architecture is a TypeScript monorepo managed by Nx and pnpm, featuring a NestJS backend (API, Worker, WebSocket), React/Next.js frontend (Dashboard, Playground), and MongoDB/Redis/ClickHouse data stores. It emphasizes extensibility through a provider factory pattern and a programmatic workflow DSL.
Matcha is a full-featured terminal email client (TUI) written in Go, using the Bubble Tea framework. It supports multiple email protocols (IMAP, JMAP, POP3, Maildir) and provides a rich set of features including PGP/SMIME encryption, OAuth2 authentication, a Lua plugin system with 35+ community plugins, background daemon for push notifications and sync, spellcheck, i18n with 11 languages, and a configurable theme system. The architecture is modular: a backend provider interface abstracts protocol implementations, a daemon runs as a background process communicating via JSON-RPC over Unix sockets, and the TUI is built with composable Bubble Tea models. The codebase demonstrates strong engineering practices with extensive test coverage, CI/CD pipelines, cross-platform packaging (Homebrew, Snap, Flatpak, Nix, WinGet), and a well-designed plugin API. It is not a data research project; it is a production-grade application.
AnonAddy (addy.io) is a self-hosted anonymous email forwarding service built with Laravel, Inertia.js, and Vue 3. In production, it allows users to create email aliases that forward to real inboxes, with support for custom domains, PGP/MIME encryption, user-defined rules (sender/subject/header conditions with actions like block, quarantine, label), and a blocklist. The system receives inbound email via a Postfix pipe, applies rules, and either forwards, replies, or sends-from aliases with rewritten headers, List-Unsubscribe banners, and optional DKIM signing. Outbound sending handles VERP bounce tracking and stores failed deliveries with deduplication. The architecture is a monolith Laravel application with a REST JSON API (used by mobile/extension clients) and a server-driven SPA frontend. Key entry points include the ReceiveEmail console command, the CustomMailer driver, and numerous API controllers under /api/v1/. The frontend uses reusable Vue components and Inertia form handling across pages for alias, recipient, domain, rule, blocklist, and settings management.
DockYard/elixir-mail is an Elixir library for building, parsing, and rendering email messages according to RFC 2822 and related MIME standards. It provides a composable API to create simple and multipart email messages, handle various transfer encodings (Base64, Quoted-Printable, 7bit, 8bit, binary), and parse incoming email into structured data. The library is structured around a core `Mail.Message` struct with separate modules for encoding, parsing, rendering, and MIME type lookup. It does not require any external runtime dependencies beyond the Erlang/OTP standard library.
This is a PHP library for parsing MIME email messages conforming to RFC 822/2822/5322. It wraps the `mailparse` PECL extension to provide a clean, object-oriented API for extracting headers, plain text and HTML bodies, attachments, and embedded content from raw email data (file, string, or stream). The library features a middleware system for custom MIME part processing, configurable attachment filename conflict strategies (suffix, random, throw), charset decoding with an extensive alias map, and type-safe enums for body type and filename strategy. It is designed for use in webmail clients, email processing pipelines, and Postfix integration, with support for complex MIME structures including multipart/alternative, inline images, and nested RFC822 messages. The test suite includes over 30 real-world email fixtures covering edge cases, making the library robust enough for production use.
This repository is the official Twilio SendGrid Java SDK, providing a comprehensive client library for the SendGrid v3 Web API. Its primary purpose is to enable Java applications to send transactional and marketing emails, manage suppression lists, retrieve email statistics, and interact with all other SendGrid API endpoints. The library is designed as a thin HTTP client wrapper, with a core `SendGrid` class that accepts an API key and exposes synchronous (`api()`) and asynchronous (`attempt()`) methods for making REST calls. A high-level `Mail` helper simplifies building complex email payloads with personalizations, attachments, tracking settings, and templates. The architecture follows a clean separation: the `BaseInterface` handles HTTP client configuration, rate limiting (automatic retry on 429), data residency (EU/global regions), and subuser impersonation. The `Request`/`Response` POJOs provide a uniform interface for all API calls. The library includes a robust event webhook verification module (`EventWebhook.java`) using ECDSA signatures, and a builder pattern for attachments that supports both `InputStream` and `String` content. External dependencies include Jackson for JSON serialization, Bouncy Castle for cryptography, and Apache Commons Codec. The codebase is well-structured with extensive examples covering all major API endpoints, unit tests using JUnit 4 and Mockito, and CI/CD via GitHub Actions. While the test file is large and repetitive, the core abstractions are clean and the library is actively maintained. It is not a data research or analytics tool; it is purely an API client library intended for integration into Java applications.
FairEmail is a fully-featured, open-source, privacy-oriented email client for Android. It supports IMAP, POP3, SMTP, OpenPGP, S/MIME, and OAuth for major providers (Gmail, Outlook, Yahoo). The app is built as a standard Android application with Activities, Fragments, Services, and WorkManager workers. It uses Room for local persistence, LiveData for reactive UI, and a custom async pattern (SimpleTask) for background operations. The codebase is notable for its extensive use of vendored libraries: it includes modified copies of JavaMail (javax.mail, com.sun.mail), AndroidX internals (Room, Paging, Emoji2, RecyclerView Selection), Google Protocol Buffers, and native language/encoding detection engines (CLD3, compact_enc_det). This hybrid approach provides deep email protocol support and privacy features like tracker blocking, certificate transparency, and DANE, but also introduces maintenance overhead and potential drift from upstream versions. The app integrates AI features (Gemini, OpenAI) for summarization and rule actions, and includes a full rule/filter engine. Despite the heavy vendoring, the core application code demonstrates solid engineering with clean abstractions, custom views that work around Android platform bugs, and a consistent async pattern. The repository is actively maintained with frequent releases and responsive issue triage.
Macro is a large open-source monorepo (AGPLv3) for an all-in-one collaborative productivity platform that unifies email, messaging, documents, tasks, CRM, AI agents, and more. The backend consists of 42+ Rust microservices following a consistent hexagonal architecture (domain/inbound/outbound), with PostgreSQL, OpenSearch, Redis, S3, Kafka/SQS/EventBridge for data storage and event-driven processing. The frontend is a SolidJS single-page application with a heavily customized Lexical editor, block-based content system, real-time collaboration via CRDT (Loro), and Tauri-based desktop/iOS apps. AI is a first-class feature with agent harnesses, MCP integration, and an AI editing worker. Infrastructure is managed via Pulumi and Docker Compose for local development. The codebase demonstrates high engineering craftsmanship with consistent patterns, extensive testing, and comprehensive observability, though the sheer scale and volume of generated code introduce some maintenance overhead.
Kurrier is a self-hosted unified communication platform designed to aggregate email, calendars, contacts, and cloud storage into a single workspace. It functions as a multi-tenant SaaS application, supporting various protocols including IMAP/SMTP for email, CalDAV/CardDAV for scheduling and contacts, and WebDAV/S3 for file storage. The system emphasizes data ownership and privacy, allowing users to manage multiple email identities and storage volumes within isolated workspaces. The architecture follows a monorepo structure with a clear separation of concerns. The frontend (`apps/web`) is built on Next.js 16 with React 19, utilizing Server Actions for business logic and a Nitro-based worker (`apps/worker`) for background jobs like IMAP sync and email delivery. Data persistence is handled by PostgreSQL with Drizzle ORM, while Redis manages job queues and caching. The platform integrates with external providers via a strategy pattern, supporting services like Google Workspace, AWS SES, and various SMTP providers. Key components include a robust provider abstraction layer for pluggable email and storage backends, a centralized encryption vault for sensitive credentials, and a standardized Server Action wrapper for consistent error handling. The codebase demonstrates high craftsmanship in its sync logic and multi-tenancy implementation, though it carries some technical debt related to type safety and complex DAV/IMAP state management.
Notifme SDK is a Node.js library for sending transactional notifications across multiple channels (email, SMS, push, webpush, Slack, WhatsApp, voice). It provides a unified interface with a provider pattern, allowing users to configure one or more providers per channel with built-in multi-provider strategies (fallback, round-robin, no-fallback). The library handles authentication, request formatting, and error handling for each provider, and includes a development mode with a notification catcher for local testing. The architecture is centered around a Sender class that dispatches requests to channel-specific strategies, which in turn call provider instances. External dependencies include nodemailer, node-fetch, web-push, winston, and node-pushnotifications. The codebase uses Flow for type checking and Babel for transpilation, with comprehensive Jest tests achieving 100% coverage thresholds.