TL;DR
Remails is an open-source Mail Transfer Agent (MTA) developed to run entirely in Europe and aimed at transactional emails like password resets and verification codes. The project evolved from a single-binary VPS proof-of-concept into a managed Kubernetes deployment that gives the team control over outbound IP addresses and high availability.
What happened
A year-long effort produced Remails, a European-hosted MTA whose code is published on GitHub and which is also available as a hosted instance at remails.net. The team began with a minimal proof of concept: a single binary running in a container on a low-cost VPS, paired with a simple PostgreSQL container and Docker Compose orchestration. As requirements shifted toward production readiness and European-only infrastructure, the stack moved to a managed Kubernetes cluster with a cloud-managed Postgres database. The application was split into a web API and SMTP components to enable replication and load-balancing for high availability. To address deliverability and reputation concerns, the architects redesigned the outbound path: SMTP outbound runs as a DaemonSet with host-network access so outbound IPs can be selected per message, a Cloud IP manager assigns provider-owned IP addresses to nodes, and a lightweight broadcast message bus forwards send requests and status updates to outbound agents.
Why it matters
- Provides an MTA option hosted entirely in Europe, responding to organizations reassessing dependencies on non-European infrastructure.
- Control over outbound IPs helps customers manage reputation and inbox deliverability independently from cloud provider shared addresses.
- An architecture focused on high availability and managed services reduces operational overhead for organizations that need reliable transactional email.
- Open-source code and a self-hosting option increase transparency and allow institutions to run the service under their own governance model.
Key facts
- Remails is intended primarily for transactional emails (verification codes, password resets, personal notifications), not for large-scale broadcast marketing.
- The project is open source with its source code available on GitHub and a hosted instance offered at remails.net.
- Initial development used a single VPS running a single binary in a container with Docker Compose alongside a PostgreSQL container.
- The production architecture uses a managed Kubernetes cluster and a managed Postgres service provided by the cloud vendor; the database is external to the cluster.
- Application components were split into a Web API and SMTP functionality to allow replication and load balancing for availability.
- Data protection measures include cloud-provider Point In Time Recovery (PITR) and a daily full backup stored at an independent location with observability alarms for failures.
- To control outbound IP reputation, the team uses BYOIP (bring your own IP) through a European cloud provider (UpCloud) and implemented a Cloud IP manager.
- SMTP outbound runs as a Kubernetes DaemonSet with host-network access so each node’s outbound agent can select from IP addresses assigned to that node.
- A lightweight, best-effort broadcast message bus carries send notifications (message ID plus chosen outbound IP) to outbound agents, which filter and act on messages and return status updates.
What to watch next
- Adoption levels of the hosted remails.net instance and community uptake of the open-source repository (confirmed in the source).
- Whether Remails will remove its restriction on broadcast or bulk email use — not confirmed in the source.
- How customer-controlled outbound IP reputations perform over time and whether high-volume customers will require additional isolation — not confirmed in the source.
- Further evolution of the message bus design and whether delivery guarantees will be added to replace the current best-effort approach — not confirmed in the source.
Quick glossary
- Mail Transfer Agent (MTA): A server-side application that routes, forwards and delivers email between mail servers using SMTP.
- Kubernetes: An orchestration system for automating deployment, scaling and management of containerized applications across clusters of machines.
- DaemonSet: A Kubernetes workload that ensures a copy of a specific pod runs on every node (or a subset of nodes) in a cluster.
- BYOIP (Bring Your Own IP): A cloud provider feature that allows a customer to use and manage their own IP address blocks within the provider’s network.
- Point-in-Time Recovery (PITR): A backup capability that allows restoring a database to a specific moment in time, often used to recover from data corruption or accidental deletion.
Reader FAQ
Is Remails open source?
Yes. The project’s source code is available on GitHub (confirmed in the source).
Can organizations self-host Remails?
Yes. The source is available for self-hosting and the team also provides a hosted instance at remails.net (confirmed in the source).
Is Remails suitable for marketing or broadcast email campaigns?
No. The project is currently focused on transactional email use cases and is not intended for large-scale broadcast emails (confirmed in the source).
Which cloud provider is used for BYOIP?
The team used the Finnish cloud provider UpCloud to satisfy the bring-your-own-IP requirement (confirmed in the source).
What are the service-level commitments or pricing?
not confirmed in the source
January 15, 2026 How we built Remails: a European Mail Transfer Agent Max Software engineer Michiel Software engineer microservices web-development Increasingly more organizations are reviewing their dependencies on foreign software…
Sources
- Remails: A European Mail Transfer Agent
- Remails – Transactional email for developers — Built in Europe
- European transactional email service
- What Is an Email MTA? A Guide to Mail Transfer Agents
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