Every AI agent that deals with people eventually needs an email address, and Open Agent Email gives each one a real inbox on your own domain. Agents receive mail in proper threads, reply in place, send new messages, schedule sends up to 90 days ahead, and handle attachments, labels, search, trash and restore from one mailbox. A human approval gate can hold any outgoing message until a person clicks approve or reject, with an expiry and a full history, so a risky reply never reaches a customer unchecked. Incoming mail is screened for prompt-injection tricks and hidden text, checked against SPF, DKIM, and DMARC, and can be scanned for viruses before an agent reads it. Agents connect through a REST API with an OpenAPI file, dependency-free Python and TypeScript SDKs, the oae command line, signed webhooks, a live WebSocket stream, or 96 MCP tools for coding agents. The browser dashboard covers guided setup, inboxes, pending approvals, the outbox queue with retries, delivery metrics with bounce and complaint tracking, contacts, templates, domains with DNS verification, and API keys. Sending runs through your own relay, SES events feed suppression lists automatically, and scoped per-inbox keys limit what each agent may do. 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.

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.

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.

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.

Your application already knows how to send mail through Amazon SES; NitroMTA lets it keep that code, change the endpoint and keys, and deliver from IP addresses you actually control. The engine answers a submission only after the message is committed to disk, so accepted mail survives a crash, a power cut, and even the loss of its host when the disk survives. Capture mode runs the whole engine locally and shows each message in a browser at port 9090 instead of sending it, which makes testing painless before any DNS exists. Out in production, new IPs warm up receiver by receiver from fifty messages a day, rising after clean days and backing off when complaints, bounces, or throttling climb. Each provider gets its own connection limits and cooldowns, hard bounces and spam complaints suppress the address automatically, and outgoing mail is DKIM-signed and sent over TLS with MTA-STS and DANE verified where published. Templates, identities, configuration sets, tenants, dedicated IPs, and SES-shaped events through an SNS subset cover the SES surface your tooling expects, and a CLI explains why any given message is still waiting. 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.

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.

Development teams hand their outgoing webhooks to Svix, which delivers each event to customer endpoints with retries, signed payloads, and a delivery record for every attempt. Your app makes one API call when something happens, a user signs up, an invoice is paid, a build finishes, and Svix delivers the event to every subscribed endpoint your customers registered. Endpoints that fail get automatic retries on a schedule, deliveries are logged attempt by attempt, and failed messages can be resent instead of vanishing. Customers organize their integrations as applications, subscribe endpoints to the event types they care about, filter by channels, and verify signed payloads so forged requests get rejected. You define the event catalog once, and fanout, throttling, and endpoint bookkeeping stop being code you maintain. Official libraries for nine languages and a CLI make the first integration an afternoon task, and the whole service runs from a Docker Compose stack with Postgres and Redis when you want it on your own infrastructure. Your product gains the webhook system customers expect, without your team becoming a deliverability department. 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.

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.

Your scanner still emails PDFs, your backup scripts still send nightly reports, and none of them will ever learn OAuth 2.0: Email OAuth 2.0 Proxy learns it on their behalf. It listens on local IMAP, POP, and SMTP ports on your server, and when a client logs in the old-fashioned way with a username and password, the proxy swaps that exchange for a modern SASL XOAUTH2 token before the connection ever reaches the provider. The client never knows anything changed, so ancient mail apps, embedded devices, monitoring tools, and hand-rolled scripts keep sending and fetching mail through Outlook, Office 365, Gmail, Google Workspace, Fastmail, Yahoo, AOL, and any other provider that demands OAuth 2.0. The hop from your client to the proxy stays simple, while the proxy opens a fully encrypted TLS connection upstream, including STARTTLS negotiation for SMTP relays that require it. One proxy instance serves many accounts at once, with each mailbox mapped to its own local port and its tokens cached under a password you control. Optional plugins can even rewrite traffic in flight: strip Microsoft Defender Safe Links back to their real URLs, stop duplicate sent messages, or swallow test mail into a black hole. Setup is a single configuration file covering server ports, per-account scopes, and token endpoints, and the proxy then runs quietly as a headless service. 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.

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.