diff --git a/explode_mbox.py b/explode_mbox.py
new file mode 100644
index 0000000..a70ce66
--- /dev/null
+++ b/explode_mbox.py
@@ -0,0 +1,86 @@
+import argparse
+import hashlib
+import os
+import pathlib
+import sys
+import typing
+
+DEBUG = os.environ.get("DEBUG") == "enabled"
+
+
+def main(sysargs=sys.argv[:]) -> int:
+    parser = argparse.ArgumentParser()
+    parser.add_argument("mbox", type=argparse.FileType("rb"))
+    parser.add_argument("output_directory", type=pathlib.Path)
+
+    args = parser.parse_args(sysargs[1:])
+
+    for msg in _iter_mbox(args.mbox):
+        if msg.length < 2:
+            print("skipping invalid message")
+            continue
+        dest = args.output_directory / msg.relpath
+        dest.parent.mkdir(parents=True, exist_ok=True)
+        print(f"writing message to {dest}")
+        dest.write_bytes(msg.as_bytes())
+    return 0
+
+
+class Message:
+    def __init__(self):
+        self.lines = []
+
+    def as_bytes(self) -> bytes:
+        return b"".join([l for l in self.lines])
+
+    @property
+    def length(self) -> int:
+        return len(self.lines)
+
+    @property
+    def signature(self) -> str:
+        return hashlib.sha512(self.lines[0]).hexdigest()
+
+    @property
+    def relpath(self) -> str:
+        sig = self.signature
+        return os.path.sep.join(
+            [sig[0:1], sig[1:3], sig[3:5], sig[5:7], f"{sig}.email"]
+        )
+
+
+def _iter_mbox(mbox: typing.BinaryIO) -> typing.Generator[Message, None, None]:
+    msg = Message()
+    cur_line = b""
+
+    while True:
+        byte = mbox.read(1)
+        if len(byte) == 0:
+            _debug(f"reached EOF")
+            msg.lines.append(cur_line)
+            yield msg
+            return
+
+        cur_line += byte
+
+        if byte != b"\n":
+            continue
+
+        if cur_line.startswith(b"From "):
+            _debug(f"reached new msg")
+            yield msg
+            msg = Message()
+
+        _debug(f"appending line {cur_line}")
+        msg.lines.append(cur_line)
+        cur_line = b""
+
+
+def _debug(msg):
+    if not DEBUG:
+        return
+    print(f"DEBUG: {msg}", file=sys.stderr)
+
+
+if __name__ == "__main__":
+    sys.exit(main())