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


     MailConverter.exe to-msg|to-mime [--ignore] <input path or mask> <output dir>

      -i, --ignore  Errors during conversion do not terminate the batch operation.
                    Optional argument.

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

    Exit codes:
     0 - Successfully converted all input files.
     1 - The conversion did not start (bad arguments or invalid input).
     2 - An error occurred during the conversion.

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

1.1.0 (2021-08-30)

  • Added switch --ignore to skip errors during batch conversion.
  • Exit-code 2 is now returned for an error during coversion.

1.0.0 (2020-07-28)

  • Enhanced compatibility.

1.0.0 (2019-06-20)

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

1.0.0 (2019-06-06)

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

1.0.0 (2019-04-12)

  • Added support for multi-file conversion.

1.0.0 (2016-07-01)

  • First standalone version released on labs.

1.0.0 (2011-02-11)

  • 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.