MailSharp

A self-hosted email server built with C# and .NET 10, providing SMTP, IMAP, and POP3 services with an integrated web management interface.

Features

• SMTP — ports 25, 587 (STARTTLS), and 465 (TLS); DKIM signing/verification; SPF and DMARC checking; relay support; configurable email flow policies per IP group
• IMAP — ports 143 (STARTTLS) and 993 (TLS); IDLE, ACL, QUOTA, SORT extensions; public folder support
• POP3 — ports 110 and 995 (TLS)
• Web Manager — ASP.NET Core Razor Pages dashboard for server status, domain management, and configuration; role-based access (User / Administrator)
• DNS — built-in async DNS resolver with configurable upstream servers
• IP Groups — per-CIDR access control with per-protocol and per-email-flow policies, expiry support
• Anti-spam / Anti-virus — pluggable per IP group

Project Structure

Getting Started

Prerequisites

• .NET 10 SDK
• A valid TLS certificate (.pfx) for your mail domain

Build and run

git clone https://github.com/alphons/MailSharp.git
cd MailSharp
dotnet run --project MailSharp.WebManager

The web interface is available at https://localhost:5001.

Default admin credentials: admin / admin — change these before exposing the server externally.

Install as a Windows Service

Run _install.cmd as Administrator from the published output directory. The script creates and starts a MailSharp Windows Service configured for delayed auto-start with automatic restart on failure.

To remove the service, run _uninstall.cmd as Administrator.

Configuration

All server settings are stored in mailsharp.json alongside the executable. The web manager provides a UI for most settings; appsettings.json controls logging and ASP.NET host options only.

Key sections in mailsharp.json

IpGroups — define CIDR ranges with per-protocol access and email flow policies:

{
  "Name": "Remote",
  "Priority": 3,
  "Cidr": "0.0.0.0/0",
  "Access": { "Smtp": true, "Pop3": false, "Imap": true, "RequireSslTlsForAuth": true },
  "EmailFlows": {
    "ExternalToLocal": { "Allowed": true, "RequireAuth": false },
    "LocalToExternal": { "Allowed": false, "RequireAuth": true }
  }
}

SmtpSettings — ports, TLS certificate, local domains, relay, DKIM, storage paths, connection limits.

Pop3Settings / ImapSettings — ports, TLS certificate, connection limits, IMAP extensions.

MailboxSettings — path where mailboxes are stored on disk.

MaintenanceUsers — web manager accounts with roles and optional expiry.

License

MIT

Contributing

Fork the repository, create a feature branch, and open a pull request.