diff --git a/.gitignore b/.gitignore
index 434ee8ad1..c485eb0cc 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,2 @@
 .worktrees
+secret_fixtures/
diff --git a/backend/main.py b/backend/main.py
new file mode 100644
index 000000000..85745bc2b
--- /dev/null
+++ b/backend/main.py
@@ -0,0 +1,16 @@
+from fastapi import FastAPI
+from fastapi.middleware.cors import CORSMiddleware
+
+app = FastAPI(title="AI Email Client API")
+
+app.add_middleware(
+    CORSMiddleware,
+    allow_origins=["http://localhost:3000"],
+    allow_credentials=True,
+    allow_methods=["*"],
+    allow_headers=["*"],
+)
+
+@app.get("/")
+def read_root() -> dict[str, str]:
+    return {"status": "ok", "message": "AI Email Client API"}
\ No newline at end of file
diff --git a/backend/requirements.txt b/backend/requirements.txt
new file mode 100644
index 000000000..4d7b0ddd2
--- /dev/null
+++ b/backend/requirements.txt
@@ -0,0 +1,4 @@
+fastapi==0.109.0
+uvicorn==0.27.0
+pytest==8.0.0
+httpx==0.26.0
\ No newline at end of file
diff --git a/backend/services/__init__.py b/backend/services/__init__.py
new file mode 100644
index 000000000..e69de29bb
diff --git a/backend/services/archive.py b/backend/services/archive.py
new file mode 100644
index 000000000..4461a29f2
--- /dev/null
+++ b/backend/services/archive.py
@@ -0,0 +1,82 @@
+import asyncio
+import zipfile
+from pathlib import Path
+
+from .exceptions import InvalidArchiveError, ArchiveSizeExceededError, ArchiveFileCountExceededError
+
+MAX_EXTRACT_SIZE = 10 * 1024 * 1024 * 1024  # 10 GB
+MAX_FILE_COUNT = 100000
+
+def extract_backup(zip_path: str | Path, output_dir: str | Path) -> list[Path]:
+    """
+    Extracts a zip archive to the specified output directory.
+    
+    WARNING: This function performs blocking I/O operations. When called from
+    an async web layer (e.g. FastAPI), it must be executed in a thread pool using
+    `fastapi.concurrency.run_in_threadpool` or `asyncio.to_thread()`.
+    
+    Args:
+        zip_path: The path to the zip archive to extract.
+        output_dir: The directory where the contents should be extracted.
+        
+    Returns:
+        A list of Path objects for the extracted files (excluding directories).
+        
+    Raises:
+        InvalidArchiveError: If the zip file is not found or corrupted.
+        ArchiveSizeExceededError: If the uncompressed size exceeds the maximum allowed limit.
+        ArchiveFileCountExceededError: If the archive exceeds the maximum allowed file count.
+    """
+    zip_path = Path(zip_path)
+    output_dir = Path(output_dir).resolve()
+    
+    output_dir.mkdir(parents=True, exist_ok=True)
+    extracted_paths = []
+    
+    try:
+        with zipfile.ZipFile(zip_path, 'r') as z:
+            total_size = 0
+            file_count = 0
+            
+            for info in z.infolist():
+                if info.is_dir():
+                    continue
+
+                file_count += 1
+                if file_count > MAX_FILE_COUNT:
+                    raise ArchiveFileCountExceededError(f"Archive exceeds maximum allowed file count of {MAX_FILE_COUNT}.")
+                
+                # Sanitize path to prevent traversal
+                parts = [p for p in info.filename.replace('\\', '/').split('/') if p not in ('', '.', '..')]
+                if not parts:
+                    continue
+                safe_name = "/".join(parts)
+                
+                target_path = (output_dir / safe_name).resolve()
+                
+                # Double-check that it is within output_dir
+                if not str(target_path).startswith(str(output_dir)):
+                    continue
+                
+                target_path.parent.mkdir(parents=True, exist_ok=True)
+                
+                with z.open(info) as source, open(target_path, "wb") as target:
+                    while chunk := source.read(8192):
+                        total_size += len(chunk)
+                        if total_size > MAX_EXTRACT_SIZE:
+                            raise ArchiveSizeExceededError(f"Archive exceeds maximum allowed extraction size of {MAX_EXTRACT_SIZE} bytes.")
+                        target.write(chunk)
+                
+                extracted_paths.append(target_path)
+                    
+    except (zipfile.BadZipFile, FileNotFoundError) as e:
+        raise InvalidArchiveError(f"Failed to extract archive: {e}") from e
+        
+    return extracted_paths
+
+async def extract_backup_async(zip_path: str | Path, output_dir: str | Path) -> list[Path]:
+    """
+    Async wrapper for extract_backup to be used safely in async contexts.
+    """
+    return await asyncio.to_thread(extract_backup, zip_path, output_dir)
+
diff --git a/backend/services/exceptions.py b/backend/services/exceptions.py
new file mode 100644
index 000000000..9ef033232
--- /dev/null
+++ b/backend/services/exceptions.py
@@ -0,0 +1,15 @@
+class ArchiveError(Exception):
+    """Base exception for archive operations."""
+    pass
+
+class InvalidArchiveError(ArchiveError):
+    """Raised when an archive is invalid, corrupted, or not found."""
+    pass
+
+class ArchiveSizeExceededError(ArchiveError):
+    """Raised when an archive exceeds the maximum allowed extracted size."""
+    pass
+
+class ArchiveFileCountExceededError(ArchiveError):
+    """Raised when an archive exceeds the maximum allowed number of files."""
+    pass
diff --git a/backend/tests/__init__.py b/backend/tests/__init__.py
new file mode 100644
index 000000000..e69de29bb
diff --git a/backend/tests/test_archive.py b/backend/tests/test_archive.py
new file mode 100644
index 000000000..f08149b06
--- /dev/null
+++ b/backend/tests/test_archive.py
@@ -0,0 +1,92 @@
+import os
+import zipfile
+import pytest
+import asyncio
+from pathlib import Path
+
+from services.archive import extract_backup, extract_backup_async
+from services.exceptions import InvalidArchiveError, ArchiveSizeExceededError, ArchiveFileCountExceededError
+
+def test_extract_backup_success(tmp_path):
+    zip_path = tmp_path / "test.zip"
+    with zipfile.ZipFile(zip_path, 'w') as z:
+        z.writestr("test.eml", b"Subject: Test Email")
+        z.writestr("folder/", b"")
+        z.writestr("folder/test2.eml", b"Subject: Test Email 2")
+    
+    out_dir = tmp_path / "output"
+    extracted_files = extract_backup(zip_path, out_dir)
+    
+    # Check only files are returned, not directories
+    assert len(extracted_files) == 2
+    assert any(f.name == "test.eml" for f in extracted_files)
+    assert any(f.name == "test2.eml" for f in extracted_files)
+    assert not any(f.name == "folder" for f in extracted_files)
+    
+    for f in extracted_files:
+        assert f.exists()
+        assert f.is_file()
+
+def test_extract_backup_file_not_found(tmp_path):
+    with pytest.raises(InvalidArchiveError, match="Failed to extract archive"):
+        extract_backup(tmp_path / "missing.zip", tmp_path / "output")
+
+def test_extract_backup_bad_zip_file(tmp_path):
+    bad_zip = tmp_path / "bad.zip"
+    bad_zip.write_text("This is not a zip file")
+    
+    with pytest.raises(InvalidArchiveError, match="Failed to extract archive"):
+        extract_backup(bad_zip, tmp_path / "output")
+
+def test_extract_backup_size_exceeded(tmp_path, monkeypatch):
+    import services.archive
+    monkeypatch.setattr(services.archive, "MAX_EXTRACT_SIZE", 10) # 10 bytes limit
+    
+    zip_path = tmp_path / "test.zip"
+    with zipfile.ZipFile(zip_path, 'w') as z:
+        z.writestr("large.txt", b"A" * 20) # 20 bytes
+    
+    with pytest.raises(ArchiveSizeExceededError, match="Archive exceeds maximum allowed extraction size"):
+        extract_backup(zip_path, tmp_path / "output")
+
+def test_extract_backup_malformed_path(tmp_path):
+    zip_path = tmp_path / "malformed.zip"
+    with zipfile.ZipFile(zip_path, 'w') as z:
+        # Create a file with a relative path trying to escape directory
+        z.writestr("../malformed.eml", b"Subject: Malformed Email")
+    
+    out_dir = tmp_path / "output"
+    extracted_files = extract_backup(zip_path, out_dir)
+    
+    assert len(extracted_files) == 1
+    assert extracted_files[0].name == "malformed.eml"
+    assert ".." not in str(extracted_files[0])
+    for f in extracted_files:
+        assert f.exists()
+        assert f.is_file()
+
+def test_extract_backup_file_count_exceeded(tmp_path, monkeypatch):
+    import services.archive
+    monkeypatch.setattr(services.archive, "MAX_FILE_COUNT", 2)
+    
+    zip_path = tmp_path / "test_count.zip"
+    with zipfile.ZipFile(zip_path, 'w') as z:
+        z.writestr("file1.txt", b"1")
+        z.writestr("file2.txt", b"2")
+        z.writestr("file3.txt", b"3")
+        
+    with pytest.raises(ArchiveFileCountExceededError, match="Archive exceeds maximum allowed file count"):
+        extract_backup(zip_path, tmp_path / "output")
+
+def test_extract_backup_async(tmp_path):
+    zip_path = tmp_path / "test_async.zip"
+    with zipfile.ZipFile(zip_path, 'w') as z:
+        z.writestr("test.eml", b"Subject: Test Email")
+        
+    out_dir = tmp_path / "output"
+    extracted_files = asyncio.run(extract_backup_async(zip_path, out_dir))
+    
+    assert len(extracted_files) == 1
+    assert extracted_files[0].name == "test.eml"
+    assert extracted_files[0].exists()
+
diff --git a/backend/tests/test_main.py b/backend/tests/test_main.py
new file mode 100644
index 000000000..893bbe7ad
--- /dev/null
+++ b/backend/tests/test_main.py
@@ -0,0 +1,9 @@
+from fastapi.testclient import TestClient
+from main import app
+
+client = TestClient(app)
+
+def test_read_root():
+    response = client.get("/")
+    assert response.status_code == 200
+    assert response.json() == {"status": "ok", "message": "AI Email Client API"}
\ No newline at end of file