diff --git a/tools/mail/mbox_to_emls.py b/tools/mail/mbox_to_emls.py
new file mode 100644
index 0000000..54f6471
--- /dev/null
+++ b/tools/mail/mbox_to_emls.py
@@ -0,0 +1,98 @@
+#!/usr/bin/env python3
+# Copyright (c) Microsoft Corporation.
+# Licensed under the MIT License.
+
+"""
+Convert an mbox file into a directory of individual .eml files.
+
+Usage:
+    python tools/mbox_to_emls.py mailbox.mbox output_dir/
+"""
+
+import argparse
+from email.utils import parsedate_to_datetime
+import mailbox
+import os
+import sys
+
+
+def make_filename(date_header: str | None, used_names: set[str]) -> str:
+    """
+    Generate a unique filename from the Date header.
+
+    Format: YYYYMMDD_HHMMSS.eml, with _NNN suffix for disambiguation.
+    Falls back to 'unknown_NNNNNN' if no valid date.
+    """
+    base = "unknown"
+    if date_header:
+        try:
+            dt = parsedate_to_datetime(date_header)
+            base = dt.strftime("%Y%m%d_%H%M%S")
+        except (ValueError, TypeError):
+            pass
+
+    # Find a unique name
+    if base == "unknown":
+        # For unknown dates, use a 6-digit serial
+        serial = 0
+        while True:
+            name = f"{base}_{serial:06d}.eml"
+            if name not in used_names:
+                used_names.add(name)
+                return name
+            serial += 1
+    else:
+        # Try without suffix first
+        name = f"{base}.eml"
+        if name not in used_names:
+            used_names.add(name)
+            return name
+        # Add serial suffix for duplicates
+        serial = 1
+        while True:
+            name = f"{base}_{serial:03d}.eml"
+            if name not in used_names:
+                used_names.add(name)
+                return name
+            serial += 1
+
+
+def main() -> int:
+    parser = argparse.ArgumentParser(
+        description="Convert an mbox file to a directory of .eml files."
+    )
+    parser.add_argument("input", help="Path to the input .mbox file")
+    parser.add_argument("output", help="Path to the output directory")
+    args = parser.parse_args()
+
+    mbox_path = args.input
+    output_dir = args.output
+
+    if not os.path.isfile(mbox_path):
+        print(f"Error: Input file not found: {mbox_path}", file=sys.stderr)
+        return 1
+
+    os.makedirs(output_dir, exist_ok=True)
+
+    mbox = mailbox.mbox(mbox_path)
+    used_names: set[str] = set()
+    count = 0
+
+    for message in mbox:
+        date_header = message.get("Date")
+        filename = make_filename(date_header, used_names)
+        filepath = os.path.join(output_dir, filename)
+
+        with open(filepath, "wb") as f:
+            f.write(message.as_bytes())
+
+        count += 1
+        if count % 100 == 0:
+            print(f"Processed {count} messages...", file=sys.stderr)
+
+    print(f"Wrote {count} .eml files to {output_dir}", file=sys.stderr)
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())