Email.Smtp 1.3.1

Email.Smtp

Transactional email for .NET behind one IEmailService abstraction, with a config-driven provider switch: send via SMTP (MailKit) or the Resend HTTP API by flipping a single config value — zero code change. Compatible with Mailpit (dev), self-hosted Maddy/Postal, any standard SMTP server, or Resend.

Features

• One IEmailService abstraction, multiple transports (Email:Provider = Smtp | Resend | Postmark)
• MailKit-based SMTP sending (replaces deprecated System.Net.Mail.SmtpClient)
• Resend HTTP API provider for high-deliverability managed sending
• Code-based HTML email templates (embedded resources)
• {{Placeholder}} template rendering with caching
• SSL/TLS support for production SMTP servers
• Optional authentication (skip for Mailpit in dev)
• Shared email_sent / email_failed log tokens across every provider (Loki-greppable)

Provider selection (config-driven, zero code change)

Register once with AddTransactionalEmail(IConfiguration) and switch transports via config:

// In Program.cs — reads Email:Provider, defaults to Smtp when absent
builder.Services.AddTransactionalEmail(builder.Configuration);

// SMTP (default) — options read from the existing "Smtp" section
{
  "Email": { "Provider": "Smtp" },
  "Smtp": { "Host": "mailpit", "Port": 1025, "UseSsl": false,
            "FromAddress": "noreply@localhost", "FromName": "SaaS Platform" }
}

// Resend — flip Provider, add the Email:Resend section, no code change
{
  "Email": { "Provider": "Resend" },
  "Email:Resend": {
    "ApiKey": "re_xxx",                       // secret; supply via env/secret store
    "FromAddress": "noreply@dloizides.com",   // must be a Resend-verified domain
    "FromName": "SaaS Platform"
  }
}

Postmark is a reserved provider value (recognised by the switch) but not yet implemented — selecting it throws a clear NotSupportedException. You can also register a single provider directly with AddSmtpEmail(...) or AddResendEmail(...).

Templates Included

Usage

// In Program.cs or DI setup
builder.Services.AddSmtpEmail(options =>
    builder.Configuration.GetSection("Smtp").Bind(options));

// In appsettings.json
{
  "Smtp": {
    "Host": "mailpit",     // or "postal.yourdomain.com"
    "Port": 1025,          // or 587 for TLS
    "UseSsl": false,
    "FromAddress": "noreply@localhost",
    "FromName": "SaaS Platform"
  }
}

// Send a templated email
var result = await emailService.SendTemplatedAsync(
    EmailTemplateNames.OtpCode,
    new EmailRecipient { Address = "user@example.com" },
    "Your Verification Code",
    new Dictionary<string, string>
    {
        ["AppName"] = "My SaaS",
        ["Code"] = "123456",
        ["ExpiryMinutes"] = "5"
    });