MailConverter is based on


Rebex Mail Converter is a command line tool for converting mail messages between different formats.

It's free for commercial and non-commercial use.


Download - Mail Converter Application »

Download - C# source code »


    Syntax: MailConverter.exe to-msg|to-mime <input path or mask> <output dir>

    Example: MailConverter.exe to-mime C:\input\*.msg C:\output
    Example: MailConverter.exe to-msg C:\input\*.eml C:\output
    Example: MailConverter.exe to-mime C:\input\* C:\output
    Example: MailConverter.exe to-msg C:\input\* C:\output
    Example: MailConverter.exe to-mime C:\input\mail.msg C:\output
    Example: MailConverter.exe to-msg C:\input\mail.eml C:\output

Source code

MailConverter is written in C# and uses Rebex Secure Mail component. Source code for the utility itself is freely available, making it possible to easily add equivalent functionality to custom applications. To compile MailConverter, download a trial version or purchase a license.


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
  • MS-TNEF/winmail.dat - Microsoft's proprietary email extension format (input-only)

Supported attachment formats:

  • MIME (Base64, Quoted-Printable, 7bit, 8bit and binary entities)
  • UUEncode
  • Embedded OLE objects within TNEF/winmail.dat e-mail messages
  • MS-TNEF/winmail.dat - Microsoft's proprietary email extension format (input-only)


MailConverter runs on:

  • Windows 10, 8.1, 8, or 7 SP1.
  • Windows Server 2012 or later.
  • Windows XP, Vista, 7, Server 2003 or 2008. You might have to install .NET 4.0 first when using the tool on these older systems.

Version history


  • Enhanced compatibility.


  • Exit-code 1 is now returned even on a generic exception.


  • Command line syntax changed. Exit-code 1 is now returned on error.


  • Added support for multi-file conversion.


  • First standalone version released on labs.


  • First version of MailConverter released as a sample for Rebex Secure Mail component.


Have a feature request or a question? Contact us or ask at Rebex Q&A Forum.