Rebex SMTP

RebexEmail Tools.NET
Version 8.0.9673 (Jun 25, 2026)

Robust SMTP client library for secure and flexible email sending.

  • Supports TLS 1.2 and 1.3 with advanced cryptography.
  • Extensive authentication methods including OAuth 2.0 and Kerberos.
  • Handles complex email scenarios with MIME, S/MIME, and asynchronous support.
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Effortlessly send and receive emails with a comprehensive and secure .NET library.
Rebex SMTP is a .NET library designed for sending emails via SMTP servers. It includes support for security protocols, authentication modes, and MIME and S/MIME message handling. The library supports synchronous and asynchronous operations and integrates with multiple .NET platforms.

SMTP Support

Provides a straightforward API that enables sending emails with minimal code while supporting complex messages with multiple recipients and attachments.

Secure Connections

Supports SMTP connections with explicit or implicit TLS/SSL encryption, ensuring safe transmission over networks with capability to inspect and validate server certificates.

Authentication Support

Implements authentication modes such as username/password, CRAM-MD5, DIGEST-MD5, OAuth 2.0, client certificates, GSSAPI, NTLM, Kerberos, and single sign-on mechanisms.

Email Sending Features

Handles sending emails directly, via IIS pickup directory, and supports sending on behalf of others, managing replies, delivery notifications, and multiple messages in a single session.

MIME and S/MIME Handling

Includes APIs for composing and processing MIME and secure S/MIME emails with signing and signature validation based on X.509 certificates and PKCS #7 standard.

Performance Optimizations

Supports advanced SMTP protocol extensions like 8-bit and binary MIME, command pipelining, and chunking to reduce latency and optimize data transfer for large messages.

Event Handling

Provides various events including message sending progress, recipient rejection, certificate validation, and command/response monitoring.

Logging and Diagnostics

Offers detailed communication logging with customizable verbosity levels and built-in or custom log writers to troubleshoot and monitor SMTP transactions.

Proxy and Custom Socket Support

Connects through SOCKS4/5, HTTP CONNECT, SSH proxies and supports custom transport layer implementations to adapt to complex network environments.

Product Compatibility

Review the details below to ensure this product is supported within your environment.

Component Type

  • .NET

.NET Version

  • .NET 10 LTS
  • .NET 9 STS
  • .NET 8 LTS
  • .NET 5 / .NET Core 3.1
  • .NET 4.8 or earlier

.NET Platform

  • .NET Assembly
  • .NET Class
  • .NET Core 3.1 Assembly

IDE Support

  • Visual Studio