Rebex Secure Mail

SMTP, IMAP, EWS, POP3, S/MIME .NET library

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Standards and platform support

100% managed .NET code with no external dependencies 

  • Rebex Secure Mail is written in 100% managed C# code.
  • No external dependencies. It only needs .NET Framework.
  • No open source code used.
  • Fully CLS-compliant.
  • Supports any .NET language (C#, VB.NET, C++/CLI, etc.)
  • Platform-independent code. Same assemblies for both 32-bit and 64-bit applications.

.NET Framework on Windows 

Rebex Secure Mail supports the following .NET Framework platforms:

  • .NET Framework 4.8
  • .NET Framework 4.7.x
  • .NET Framework 4.6.x
  • .NET Framework 4.5.x
  • .NET Framework 4.0
  • .NET Framework 3.5 SP1
  • .NET Framework 3.5
  • .NET Framework 3.0
  • .NET Framework 2.0
  • Both 32-bit and 64-bit versions (same DLLs)

Supported IDE versions:

  • Microsoft Visual Studio 2019
  • Microsoft Visual Studio 2017
  • Microsoft Visual Studio 2015
  • Microsoft Visual Studio 2013
  • Microsoft Visual Studio 2012
  • Microsoft Visual Studio 2010
  • Microsoft Visual Studio 2008

Supported Windows versions:

  • Windows 10
  • Windows Server 2019
  • Windows Server 2016
  • Windows 8.1
  • Windows Server 2012 R2
  • Windows Server 2012
  • Windows Server 2008 R2
  • Windows Server 2008
  • Windows 7

Rebex Secure Mail is known to work on Windows 8, Windows Vista, Windows XP SP3 and Windows Server 2003 R2. However, these platforms already reached end-of-life, which means we cannot guarantee any kind of support for Rebex Secure Mail on these operating systems.

.NET Core 

Rebex Secure Mail supports .NET Core platform.

Supported frameworks:

Supported operating systems:

  • Windows 10
  • Windows 8.1
  • Windows 7 (SP1 and higher)
  • Windows Server 2008 R2 (SP1 and higher)
  • Linux (64-bit)
  • macOS (64-bit)

.NET Standard 

Rebex Secure Mail supports .NET Standard 1.5/2.0 on .NET Core 2.1 and 2.2. It also supports .NET Standard 2.0 on Mono 5.14 (or higher). Support for .NET Standard 2.0 on Universal Windows Platform (build 16299 or higher) and Xamarin.Mac (version 3.8 or higher) is experimental.

Mono on Linux 

Rebex Secure Mail supports Mono 4.x/5.x on Linux and Apple macOS (OS X).

Xamarin.iOS 

  • Visual Studio with Xamarin.iOS 10.3 or later
  • iOS 10 or later

Xamarin.Android 

  • Visual Studio with Xamarin.Android 8.0 or later

Xamarin.Mac 

Rebex Secure Mail features experimental support for Xamarin.Mac 3.8 or later via .NET Standard 2.0.

Universal Windows Platform 

Rebex Secure Mail features experimental support for Universal Windows Platform (UWP/UAP) applications on Windows 10 via .NET Standard 2.0.

Supported platforms:

  • Windows 10 (version 1709 or higher)
  • Windows 10 IoT (version 1709 or higher)

In order to use Rebex Secure Mail on these platforms, make sure to specify at least Windows 10 Fall Creators Update (10.0; Build 16299) in your Universal Windows project.

ASP.NET 

Rebex Secure Mail can be used within an ASP.NET web page. However, you have to keep in mind specific features of the ASP.NET platform (it is stateless, multithreaded, it may be limited by MediumTrust security level...).

Further info on using Rebex components in web environment can be found in How to use Rebex SFTP or FTP/SSL in ASP.NET knowledge base article. The article discusses SFTP and FTP/SSL, but implications for Rebex Secure Mail components are the same.

Legacy platform support 

For details of legacy platforms support see the following articles:

.NET Compact Framework on handhelds and mobiles 

Rebex Secure Mail supports Microsoft legacy handheld and mobile platforms.

Supported frameworks:

  • .NET Compact Framework 3.5
  • .NET Compact Framework 3.9

Supported mobile operating systems:

  • Windows CE 5.0, 6.x
  • Pocket PC
  • Windows Mobile
  • Windows Embedded Compact 7
  • Windows Embedded Compact 2013

Supported IDE versions:

  • Microsoft Visual Studio 2008
  • Microsoft Visual Studio 2012
  • Microsoft Visual Studio 2013

Internet RFC specifications 

Rebex Secure Mail aims to implement the following Internet standards:

SMTP RFCs:

POP3 RFCs:

IMAP RFCs:

MIME, S/MIME and CMS RFCs:

TLS RFCs:

Other RFCs:

While we tried hard to be compliant with relevant RFCs, current practice in Internet mail often deviates from these standards. In fact, sometimes being compliant can severely hinder interoperability with existing software. Interoperability was therefore the highest priority.

For example, being compliant with RFC 2231 would lead to incompatibility with Microsoft Outlook, Outlook Express, and possibly a number of other mail agents as well. So even though Rebex Secure Mail is able to parse RFC2231-compliant messages, it does not produce them.)

TLS/SSL versions 

Supported TLS/SSL protocol versions:

  • SSL 3.0
  • TLS 1.0
  • TLS 1.1
  • TLS 1.2

MIME, S/MIME, Outlook MSG and other email formats 

Supported e-mail message formats:

  • RFC 822/2822/5322 - Internet Message Format
  • MIME - Multipurpose Internet Mail Extensions
  • Outlook MSG - native format used by Microsoft Outlook/li>
  • MS-TNEF/winmail.dat - Microsoft's proprietary email extension format

Supported attachment subformats:

  • UUEncode
  • Embedded OLE objects within TNEF/winmail.dat e-mail messages
  • Application-specific OLE attachments in MSG e-mail messages
  • Base64, Quoted-Printable, 7bit, 8bit and binary entities in MIME e-mail messages

FIPS 140-2 mode 

Rebex Secure Mail can operate in a FIPS 140-2 compliant mode. When enabled, only FIPS-approved cryptographic modules from MS CryptoAPI are used. FIPS mode is activated automatically when Windows is running in FIPS mode. To switch on the FIPS mode manually, set
Rebex.Security.Cryptography.CryptoHelper.UseFipsAlgorithmsOnly to true.

Proxy servers 

  • SOCKS4
  • SOCKS4a (Socks4 with domain name resolving)
  • SOCKS5
  • HTTP proxies with CONNECT method support

Learn how to use proxy servers in Rebex Secure Mail.

Authentication methods 

SMTP authentication methods

  • Auto - automatically choose the best method available.
  • Plain - RFC 2595 plaintext authentication.
  • NTLM - Integrated Microsoft Windows Authentication.
  • GSSAPI - currently supported mechanisms are Kerberos, NTLM and SPNEGO/Negotiate.
  • Digest-MD5 - RFC 2831 DIGEST-MD5 authentication.
  • CRAM-MD5 - RFC 2195 CRAM-MD5 authentication.
  • Login - 'LOGIN' plaintext authentication.

POP3 authentication methods

  • Auto - automatically choose the best method available.
  • Plain - RFC 2595 plaintext authentication.
  • NTLM - Integrated Microsoft Windows Authentication.
  • GSSAPI - GSSAPI authentication (currently supported mechanisms are Kerberos, NTLM and SPNEGO/Negotiate).
  • Digest-MD5 - RFC 2831 DIGEST-MD5 authentication.
  • CRAM-MD5 - RFC 2195 CRAM-MD5 authentication.
  • Login - 'LOGIN' plaintext authentication.
  • ClearText - Legacy plaintext USER/PASS login.
  • APOP - POP3-specific challenge-response authentication.

IMAP authentication methods

  • Auto - automatically choose the best method available.
  • Plain - RFC 2595 plaintext authentication.
  • NTLM - Integrated Microsoft Windows Authentication.
  • GSSAPI - currently supported mechanisms are Kerberos, NTLM and SPNEGO/Negotiate.
  • Digest-MD5 - RFC 2831 DIGEST-MD5 authentication.
  • CRAM-MD5 - RFC 2195 CRAM-MD5 authentication.
  • Login - 'LOGIN' plaintext authentication.
  • ClearText - Legacy plaintext LOGIN command.
  • External - RFC 4422 - if the client already established its credentials via external means
See Authentication section to see how to select a specific authentication method.
Note: GSSAPI and NTLM authentication methods are only supported on Windows.

Exchange Web Services (EWS) 

The following servers currently support Exchange Web Services (EWS):

  • Microsoft Exchange 2007 and all service packs
  • Microsoft Exchange 2010 and all service packs
  • Microsoft Exchange 2013 and all service packs
  • Microsoft Exchange 2016 and all service packs
  • Microsoft Office 365 online servers
Note: Hotmail, Live.com and Outlook.com servers do not support EWS.

SMTP, IMAP, POP3 Extensions 

SMTP extensions

  • Pipelining - Sending SMTP commands in groups
  • Chunking - Enhanced method of sending message data
  • Binary MIME
  • 8bit MIME
  • ETRN - Enhanced turn command support
  • Enhanced status codes
  • DSN - Delivery status notifications
  • Message size declaration
  • STARTTLS - Explicit TLS/SSL support

IMAP extensions

  • UIDPLUS - StoreMessage method will return unique ID of the message at the server
  • LITERAL+ - The LITERAL+ extension permits IMAP clients to send commands containing 8-bit or unicode arguments without asking the server's permission to send each argument
  • IDLE/DONE command support
  • COMPRESS=DEFLATE - Deflate compression extension support
  • XLIST - Extended list - created by Google for GMail IMAP - used to retrieve folder purpose info
  • STARTTLS - Explicit TLS/SSL support
  • PREAUTH - Password-less authentication

POP3 extensions

  • APOP - an enhanced authorization method
  • STLS - Explicit TLS/SSL support

Cryptographic algorithms 

  • Diffie-Hellman key exchange
  • RSA
  • DSA (with support of non-standard key sizes of up to 4096 bits)
  • DES (legacy)
  • Tripple DES
  • ArcTwo (compatible with RC2, legacy)
  • ArcFour (compatible with RC4)
  • AES
  • MD5 (legacy)
  • SHA-1
  • SHA-2 (SHA-256, SHA-384, SHA-512)

Learn more about TLS/SSL security standards details.
Learn more about S/MIME security standards details.

Scripting platforms 

Rebex Secure Mail is designed primary for use in .NET framework applications. However, it can be used in several other scripting and hosting environments:

  • Microsoft SQL Server SSIS packages
  • Microsoft SQL Server SQL CLR stored procedures
  • Microsoft PowerShell scripts

See how to use Rebex Secure Mail in SSIS, SQL CLR and PowerShell environments.

Other technologies 

  • IPv4 and IPv6 support
  • Kerberos v5, NTLM and Negotiate (see more about GSSAPI authentication) on Windows