Context

Issue #609 surfaced a valid archival / extraction use case: callers converting Outlook .msg files sometimes need access to source headers and Outlook-specific metadata that Simple Java Mail intentionally does not copy into Email#getHeaders().

Scope

Clean up the Outlook converter API so this data is available through an explicit secondary conversion result instead of making the ignored-header list configurable.

• Add a public result type for Outlook conversions.
• Expose source .msg headers and selected Outlook metadata for archive / indexing use cases.
• Keep converted Email headers focused on headers that are safe and meaningful for the normalized Simple Java Mail model.
• Preserve compatibility for the existing conversion methods.

Fixes #609