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I wants to know the easy way to convert my MSG files into MBOX formats, without any data loss. I have lots of files to convert.

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According to RFC 4135, MBOX format stores mailbox messages in RFC 2822 format and only differs in several aspects from it:

  • Unix end-of-line sequence (0A) is used instead of Windows end-of-line sequence (0D 0A).
  • Messages must be 7-bit (no 8-bit MIME or binary MIME).
  • Each newly added message is terminated with a completely empty line.

Rebex Secure Mail already supports conversion of Outlook MSG files to the MIME format (an extension of RFC 2822), so implementing a custom utility that performs MSG to MBOX conversion should be quite simple. Our MSG-to-MIME and MIME-to-MSG conversion utility (comes with source code) could be used as a base.

Note that the lack of 8-bit MIME means that some messages, such as signed messages using 8-bit MIME or binary MIME, cannot be represented as required by RFC 4135. However, MBOX format was never formally defined (it's mostly a generic term for a family of related file formats), so this might not actually be an issue.