Graph Email Sender

A minimal C# console app that sends email via the Microsoft Graph API using app-only authentication (client credentials / service-principal flow).

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Prerequisites

Requirement	Version
.NET SDK	8.0 +
Azure AD App Registration	see below

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1 — Register an Azure AD App

1. Go to Azure Portal → Azure Active Directory → App registrations → New registration.
2. Give it a name (e.g. GraphEmailSender) and click Register.
3. Note down:
   • Application (client) ID
   • Directory (tenant) ID
4. Under Certificates & secrets → New client secret — create a secret and copy the Value.
5. Under API permissions → Add a permission → Microsoft Graph → Application permissions, add Mail.Send.
6. Click Grant admin consent for your tenant.

⚠️ Mail.Send is an application permission (not delegated).
It lets the app send mail as any user in the tenant — restrict access via an application access policy if needed.

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2 — Set Environment Variables

# Windows (PowerShell)
$env:AZURE_TENANT_ID     = "your-tenant-id"
$env:AZURE_CLIENT_ID     = "your-client-id"
$env:AZURE_CLIENT_SECRET = "your-client-secret"
$env:SENDER_EMAIL        = "sender@yourdomain.com"

# macOS / Linux
export AZURE_TENANT_ID="your-tenant-id"
export AZURE_CLIENT_ID="your-client-id"
export AZURE_CLIENT_SECRET="your-client-secret"
export SENDER_EMAIL="sender@yourdomain.com"

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3 — Run the App

cd GraphEmailSender
dotnet run

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Project Structure

GraphEmailSender/
├── GraphEmailSender.csproj   # NuGet references
├── Program.cs                # All app logic
└── README.md

Key classes in Program.cs

Class / Record	Purpose
AppConfig	Loads credentials from environment variables
GraphClientFactory	Creates GraphServiceClient with ClientSecretCredential
EmailMessage	Immutable record describing an outbound email
EmailSender	Wraps the Graph sendMail API call

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NuGet Packages

Package	Why
Microsoft.Graph	Typed Graph SDK (models + request builders)
Azure.Identity	ClientSecretCredential for app-only auth

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Customising the Email

Edit the email variable in Program.cs:

var email = new EmailMessage
{
    To      = ["alice@example.com", "bob@example.com"],
    Cc      = ["manager@example.com"],
    Subject = "Your subject here",
    Body    = "<p>HTML or plain text body</p>",
    IsHtml  = true,
};