diff --git a/.gitea/workflows/cron.yaml b/.gitea/workflows/cron.yaml
index cda5d0b..8b68ebe 100644
--- a/.gitea/workflows/cron.yaml
+++ b/.gitea/workflows/cron.yaml
@@ -18,11 +18,60 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
-      - uses: docker/setup-buildx-action@f87e5991a6d7451dcb8d9637bfbc97413f497069 # v4
-      - run: docker build -f pkg/Dockerfile -t ci-image:${{ github.sha }} .
+      - uses: actions/setup-python@5fda3b95a4ea91299a34e894583c3862153e4b97 # v7
+        with:
+          python-version: "3.13"
+      - name: Install dependencies
+        run: pip install -r requirements.txt pytest
+      - name: Run unit tests
+        run: pytest tests/ -v
+        env:
+          # indexer/server read env at import; unit tests need no real backend
+          QDRANT_URL: http://localhost:6333
+          COLLECTION_NAME: test
+
+  integration-test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
+
+      - name: Cleanup old Qdrant container
+        run: |
+          docker rm -f qdrant-${{ github.run_id }} 2>/dev/null || true
+
+      - name: Start Qdrant
+        run: |
+          docker run -d --name qdrant-${{ github.run_id }} \
+            --network "container:$(hostname)" \
+            docker.io/qdrant/qdrant:latest
+
+      - name: Wait for Qdrant
+        run: |
+          for i in $(seq 1 30); do
+            curl -s http://localhost:6333/healthz \
+              && echo "QDRANT ready" && break
+            echo "Waiting for Qdrant... ($i/30)"
+            sleep 1
+          done
+          curl -s http://localhost:6333/healthz > /dev/null
+
+      - uses: actions/setup-python@5fda3b95a4ea91299a34e894583c3862153e4b97 # v7
+        with:
+          python-version: "3.13"
+      - name: Install dependencies
+        run: pip install -r requirements.txt pytest
+      - name: Run integration tests
+        run: pytest tests/ -v -m integration
+        env:
+          QDRANT_URL: http://localhost:6333
+          COLLECTION_NAME: test_mcp_maildir
+
+      - name: Cleanup Qdrant
+        if: always()
+        run: docker rm -f qdrant-${{ github.run_id }} || true
 
   build-push:
-    needs: [test]
+    needs: [test, integration-test]
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
diff --git a/.gitea/workflows/docker-build.yaml b/.gitea/workflows/docker-build.yaml
index faf470b..8972a8e 100644
--- a/.gitea/workflows/docker-build.yaml
+++ b/.gitea/workflows/docker-build.yaml
@@ -29,8 +29,8 @@ jobs:
 
       - name: Start Qdrant
         run: |
-          docker rm -f qdrant 2>/dev/null || true
-          docker run -d --name qdrant \
+          docker rm -f qdrant-${{ github.run_id }} 2>/dev/null || true
+          docker run -d --name qdrant-${{ github.run_id }} \
             --network "container:$(hostname)" \
             docker.io/qdrant/qdrant:latest
 
@@ -49,14 +49,14 @@ jobs:
         run: |
           pip install -r requirements.txt pytest
       - name: Run integration tests
-        run: pytest tests/test_integration.py -v
+        run: pytest tests/ -v -m integration
         env:
           QDRANT_URL: http://localhost:6333
           COLLECTION_NAME: test_mcp_maildir
 
       - name: Cleanup Qdrant
         if: always()
-        run: docker rm -f qdrant 2>/dev/null || true
+        run: docker rm -f qdrant-${{ github.run_id }} 2>/dev/null || true
 
   build:
     runs-on: ubuntu-latest
diff --git a/.gitea/workflows/main.yaml b/.gitea/workflows/main.yaml
index fecf74b..a1ad96e 100644
--- a/.gitea/workflows/main.yaml
+++ b/.gitea/workflows/main.yaml
@@ -18,11 +18,60 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
-      - uses: docker/setup-buildx-action@f87e5991a6d7451dcb8d9637bfbc97413f497069 # v4
-      - run: docker build -f pkg/Dockerfile -t ci-image:${{ github.sha }} .
+      - uses: actions/setup-python@5fda3b95a4ea91299a34e894583c3862153e4b97 # v7
+        with:
+          python-version: "3.13"
+      - name: Install dependencies
+        run: pip install -r requirements.txt pytest
+      - name: Run unit tests
+        run: pytest tests/ -v
+        env:
+          # indexer/server read env at import; unit tests need no real backend
+          QDRANT_URL: http://localhost:6333
+          COLLECTION_NAME: test
+
+  integration-test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
+
+      - name: Cleanup old Qdrant container
+        run: |
+          docker rm -f qdrant-${{ github.run_id }} 2>/dev/null || true
+
+      - name: Start Qdrant
+        run: |
+          docker run -d --name qdrant-${{ github.run_id }} \
+            --network "container:$(hostname)" \
+            docker.io/qdrant/qdrant:latest
+
+      - name: Wait for Qdrant
+        run: |
+          for i in $(seq 1 30); do
+            curl -s http://localhost:6333/healthz \
+              && echo "QDRANT ready" && break
+            echo "Waiting for Qdrant... ($i/30)"
+            sleep 1
+          done
+          curl -s http://localhost:6333/healthz > /dev/null
+
+      - uses: actions/setup-python@5fda3b95a4ea91299a34e894583c3862153e4b97 # v7
+        with:
+          python-version: "3.13"
+      - name: Install dependencies
+        run: pip install -r requirements.txt pytest
+      - name: Run integration tests
+        run: pytest tests/ -v -m integration
+        env:
+          QDRANT_URL: http://localhost:6333
+          COLLECTION_NAME: test_mcp_maildir
+
+      - name: Cleanup Qdrant
+        if: always()
+        run: docker rm -f qdrant-${{ github.run_id }} || true
 
   build:
-    needs: [test]
+    needs: [test, integration-test]
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
diff --git a/.gitea/workflows/pr.yaml b/.gitea/workflows/pr.yaml
index 48735fa..47e08fd 100644
--- a/.gitea/workflows/pr.yaml
+++ b/.gitea/workflows/pr.yaml
@@ -14,9 +14,25 @@ jobs:
         with:
           dockerfile: pkg/Dockerfile
 
+  pytest:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
+      - uses: actions/setup-python@5fda3b95a4ea91299a34e894583c3862153e4b97 # v7
+        with:
+          python-version: "3.13"
+      - name: Install dependencies
+        run: pip install -r requirements.txt pytest
+      - name: Run unit tests
+        run: pytest tests/ -v
+        env:
+          # indexer/server read env at import; unit tests need no real backend
+          QDRANT_URL: http://localhost:6333
+          COLLECTION_NAME: test
+
   build-test:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
       - uses: docker/setup-buildx-action@f87e5991a6d7451dcb8d9637bfbc97413f497069 # v4
-      - run: docker build -f pkg/Dockerfile -t ci-image:${{ github.sha }} .
\ No newline at end of file
+      - run: docker build -f pkg/Dockerfile -t ci-image:${{ github.sha }} .
diff --git a/.gitea/workflows/tag.yaml b/.gitea/workflows/tag.yaml
index b90cfcd..ceb1674 100644
--- a/.gitea/workflows/tag.yaml
+++ b/.gitea/workflows/tag.yaml
@@ -18,11 +18,60 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
-      - uses: docker/setup-buildx-action@f87e5991a6d7451dcb8d9637bfbc97413f497069 # v4
-      - run: docker build -f pkg/Dockerfile -t ci-image:${{ github.sha }} .
+      - uses: actions/setup-python@5fda3b95a4ea91299a34e894583c3862153e4b97 # v7
+        with:
+          python-version: "3.13"
+      - name: Install dependencies
+        run: pip install -r requirements.txt pytest
+      - name: Run unit tests
+        run: pytest tests/ -v
+        env:
+          # indexer/server read env at import; unit tests need no real backend
+          QDRANT_URL: http://localhost:6333
+          COLLECTION_NAME: test
+
+  integration-test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
+
+      - name: Cleanup old Qdrant container
+        run: |
+          docker rm -f qdrant-${{ github.run_id }} 2>/dev/null || true
+
+      - name: Start Qdrant
+        run: |
+          docker run -d --name qdrant-${{ github.run_id }} \
+            --network "container:$(hostname)" \
+            docker.io/qdrant/qdrant:latest
+
+      - name: Wait for Qdrant
+        run: |
+          for i in $(seq 1 30); do
+            curl -s http://localhost:6333/healthz \
+              && echo "QDRANT ready" && break
+            echo "Waiting for Qdrant... ($i/30)"
+            sleep 1
+          done
+          curl -s http://localhost:6333/healthz > /dev/null
+
+      - uses: actions/setup-python@5fda3b95a4ea91299a34e894583c3862153e4b97 # v7
+        with:
+          python-version: "3.13"
+      - name: Install dependencies
+        run: pip install -r requirements.txt pytest
+      - name: Run integration tests
+        run: pytest tests/ -v -m integration
+        env:
+          QDRANT_URL: http://localhost:6333
+          COLLECTION_NAME: test_mcp_maildir
+
+      - name: Cleanup Qdrant
+        if: always()
+        run: docker rm -f qdrant-${{ github.run_id }} || true
 
   build-push:
-    needs: [test]
+    needs: [test, integration-test]
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
diff --git a/pytest.ini b/pytest.ini
index 80432c2..fe9256e 100644
--- a/pytest.ini
+++ b/pytest.ini
@@ -1,3 +1,8 @@
 [pytest]
 testpaths = tests
 pythonpath = src
+; Integration tests (tests/test_integration.py) require a live Qdrant on
+; localhost:6333 — they only run in the nightly CI job (or manually with -m integration).
+markers =
+    integration: requires a live Qdrant instance (deselected by default)
+addopts = -m "not integration" -p no:cacheprovider
diff --git a/src/indexer.py b/src/indexer.py
index 8682934..944fcc1 100644
--- a/src/indexer.py
+++ b/src/indexer.py
@@ -22,26 +22,27 @@ from bs4 import BeautifulSoup
 # Load .env config
 load_dotenv()
 
-# Configuration
+# Configuration (validated lazily in main() so the module can be imported
+# and unit-tested without environment variables)
 MAILDIR_PATH = os.environ.get("MAILDIR_PATH", "")
 MAILDIR_FOLDERS = os.environ.get("MAILDIR_FOLDERS", "")
 QDRANT_URL = os.environ.get("QDRANT_URL", "")
 COLLECTION_NAME = os.environ.get("COLLECTION_NAME", "")
 
-if not MAILDIR_PATH:
-    raise ValueError("MAILDIR_PATH environment variable is required.")
-if not QDRANT_URL:
-    raise ValueError("QDRANT_URL environment variable is required.")
-if not COLLECTION_NAME:
-    raise ValueError("COLLECTION_NAME environment variable is required.")
-
-EMBEDDING_MODEL_NAME = os.environ.get("EMBEDDING_MODEL_NAME", "BAAI/bge-small-en-v1.5")
-BATCH_SIZE = int(os.environ.get("BATCH_SIZE", "100"))
-EMBEDDING_BATCH_SIZE = int(os.environ.get("EMBEDDING_BATCH_SIZE", "64"))
 METADATA_COLLECTION = "mcp_indexer_metadata"
 INCREMENTAL_DAYS = int(os.environ.get("INCREMENTAL_DAYS", "7"))
 FORCE_REINDEX = os.environ.get("FORCE_REINDEX", "").lower() in ("1", "true", "yes")
 
+
+def _validate_config():
+    """Raises if required environment variables are missing. Called from main()."""
+    if not MAILDIR_PATH:
+        raise ValueError("MAILDIR_PATH environment variable is required.")
+    if not QDRANT_URL:
+        raise ValueError("QDRANT_URL environment variable is required.")
+    if not COLLECTION_NAME:
+        raise ValueError("COLLECTION_NAME environment variable is required.")
+
 def decode_mime_words(s: str) -> str:
     """Decodes MIME encoded strings (e.g. subjects, filenames)."""
     if not s:
@@ -251,6 +252,8 @@ def main():
     Main ingestion function.
     Reads Maildir, extracts text, generates local embeddings, and pushes to Qdrant.
     """
+    _validate_config()
+
     print(f"Indexing emails from {MAILDIR_PATH} into {QDRANT_URL}...")
 
     if not os.path.exists(MAILDIR_PATH):
diff --git a/tests/conftest.py b/tests/conftest.py
new file mode 100644
index 0000000..bcd0466
--- /dev/null
+++ b/tests/conftest.py
@@ -0,0 +1,15 @@
+"""Shared test configuration — sets env vars ONCE before any test module runs.
+
+The env must be consistent for the whole pytest session: server.py freezes
+COLLECTION_NAME/QDRANT_URL at import time, while the integration fixture
+reads os.environ at fixture time. If any test module mutates os.environ after
+that (test_server.py used to set COLLECTION_NAME='test'), the fixture creates
+a different collection than the one server functions query → 404.
+Keep all env wiring here so import order no longer matters.
+"""
+
+import os
+
+os.environ.setdefault("QDRANT_URL", "http://localhost:6333")
+os.environ.setdefault("COLLECTION_NAME", "test_mcp_maildir")
+os.environ.setdefault("EMBEDDING_MODEL_NAME", "BAAI/bge-small-en-v1.5")
diff --git a/tests/test_indexer.py b/tests/test_indexer.py
new file mode 100644
index 0000000..4b33ce7
--- /dev/null
+++ b/tests/test_indexer.py
@@ -0,0 +1,229 @@
+"""Unit tests for mcp-maildir indexer parsing functions.
+
+Pure-function tests: no Qdrant, no embedding model, no network.
+A throwaway Maildir is built in tmp_path for get_recent_keys().
+"""
+
+import mailbox
+import os
+import time
+import uuid
+from datetime import datetime, timezone, timedelta
+from email.message import EmailMessage
+from email.utils import format_datetime
+
+import pytest
+
+from indexer import (
+    decode_mime_words,
+    extract_text_from_html,
+    normalize_email_address,
+    parse_email_message,
+    get_recent_keys,
+    METADATA_COLLECTION,
+)
+
+
+# ---------------------------------------------------------------------------
+# decode_mime_words
+# ---------------------------------------------------------------------------
+
+class TestDecodeMimeWords:
+    def test_empty_and_none(self):
+        assert decode_mime_words("") == ""
+        assert decode_mime_words(None) == ""
+
+    def test_plain_ascii(self):
+        assert decode_mime_words("Hello World") == "Hello World"
+
+    def test_encoded_word_utf8(self):
+        # =?utf-8?q?...?= encoded word
+        assert decode_mime_words("=?utf-8?q?Caf=C3=A9_au_lait?=") == "Café au lait"
+
+    def test_encoded_word_iso8859(self):
+        # decode_mime_words does not strip whitespace around the words
+        assert decode_mime_words("=?iso-8859-1?q?caf=E9?=") == "café"
+
+    def test_mixed_encoded_and_plain(self):
+        assert decode_mime_words("Re: =?utf-8?q?planning_2026?=") == "Re: planning 2026"
+
+
+# ---------------------------------------------------------------------------
+# extract_text_from_html
+# ---------------------------------------------------------------------------
+
+class TestExtractTextFromHtml:
+    def test_simple_paragraphs(self):
+        html = "<html><body><p>Hello</p><p>World</p></body></html>"
+        assert extract_text_from_html(html) == "Hello World"
+
+    def test_strips_tags_and_scripts(self):
+        html = "<div>Sign<span>ature</span><script>evil()</script>End</div>"
+        text = extract_text_from_html(html)
+        assert "evil()" not in text
+        # get_text uses separator=" ", so tags become whitespace
+        assert "Sign" in text and "ature" in text and "End" in text
+
+    def test_fallback_on_invalid_content(self):
+        # Garbage that would make the parser blow up should not raise
+        assert extract_text_from_html(None) is None
+
+
+# ---------------------------------------------------------------------------
+# parse_email_message — real mailbox.Message objects (no mocks)
+# ---------------------------------------------------------------------------
+
+def build_email(
+    subject="Hello",
+    body="This is the body.",
+    html=None,
+    attachments=None,
+    charset="utf-8",
+):
+    """Builds a real EmailMessage, optionally multipart with attachments."""
+    msg = EmailMessage()
+    msg["Subject"] = subject
+    msg["From"] = "Alice <alice@example.com>"
+    msg["To"] = "Bob <bob@example.com>"
+    msg["Message-ID"] = "<build-email@example.com>"
+    msg["Date"] = format_datetime(datetime(2026, 1, 15, 10, 0, 0, tzinfo=timezone.utc))
+
+    if html:
+        msg.set_content(body)
+        msg.add_alternative(html, subtype="html")
+    else:
+        msg.set_content(body, charset=charset)
+
+    for filename, content in (attachments or {}).items():
+        payload = content if isinstance(content, bytes) else content.encode()
+        msg.add_attachment(payload, maintype="application",
+                           subtype="octet-stream", filename=filename)
+    return msg
+
+
+def build_raw_email(raw_bytes: bytes):
+    """Parses raw email bytes (for exotic headers without EmailMessage helpers)."""
+    import email as email_mod
+    return email_mod.message_from_bytes(raw_bytes)
+
+
+class TestParseEmailMessage:
+    def test_plain_text_body(self):
+        msg = build_email(body="Line one.\nLine two.")
+        body, attachments = parse_email_message(msg)
+        assert "Line one." in body and "Line two." in body
+        assert attachments == []
+
+    def test_attachments_detected_and_excluded_from_body(self):
+        msg = build_email(
+            body="See attached.",
+            attachments={"report.pdf": b"%PDF-fake", "notes.txt": b"notes"},
+        )
+        body, attachments = parse_email_message(msg)
+        assert attachments == ["report.pdf", "notes.txt"]
+        assert "%PDF" not in body
+        assert "See attached." in body
+
+    def test_html_alternative_extracts_text(self):
+        msg = build_email(
+            body="Fallback plain text.",
+            html="<html><body><b>Bold</b> intro</body></html>",
+        )
+        body, _ = parse_email_message(msg)
+        assert "Bold" in body and "intro" in body
+
+    def test_unknown_charset_falls_back_not_crash(self):
+        # A payload claiming an unknown charset must not raise.
+        # Built from raw bytes: EmailMessage.set_content(charset=...) would
+        # reject the unknown encoding at build time, real mail does not.
+        raw = (
+            b"Subject: broken charset\n"
+            b"From: alice@example.com\n"
+            b"To: bob@example.com\n"
+            b"Content-Type: text/plain; charset=x-unknown-charset\n"
+            b"Content-Transfer-Encoding: 8bit\n\n"
+            b"body with broken charset\n"
+        )
+        msg = build_raw_email(raw)
+        body, attachments = parse_email_message(msg)
+        # Whatever the fallback, we must get a string body and no exception
+        assert isinstance(body, str)
+        assert attachments == []
+
+    def test_encoded_attachment_filename_decoded(self):
+        msg = build_email(
+            body="body",
+            attachments={},
+        )
+        # Add attachment with non-ascii filename via encoded word
+        msg.add_attachment(b"data", maintype="application", subtype="pdf",
+                           filename="café-rapport.pdf")
+        body, attachments = parse_email_message(msg)
+        assert attachments == ["café-rapport.pdf"]
+
+
+# ---------------------------------------------------------------------------
+# normalize_email_address (indexer copy — same contract as server.py)
+# ---------------------------------------------------------------------------
+
+class TestIndexerNormalizeEmailAddress:
+    def test_display_name(self):
+        assert normalize_email_address("John Doe <john@example.com>") == "john@example.com"
+
+    def test_case_and_whitespace(self):
+        assert normalize_email_address("  USER@Example.COM ") == "user@example.com"
+
+    def test_empty(self):
+        assert normalize_email_address("") == ""
+        assert normalize_email_address(None) == ""
+
+
+# ---------------------------------------------------------------------------
+# get_recent_keys — real Maildir on disk (tmp_path), mtime-driven
+# ---------------------------------------------------------------------------
+
+def make_maildir(root):
+    """Opens a Maildir at root — pre-creates cur/new/tmp because mailbox.Maildir
+    (Python 3.11) does not create them when adding a message."""
+    for sub in ("cur", "new", "tmp"):
+        os.makedirs(os.path.join(str(root), sub), exist_ok=True)
+    return mailbox.Maildir(str(root), create=False)
+
+
+def write_maildir_message(maildir: mailbox.Maildir, msg: EmailMessage):
+    """Adds a message and returns its key."""
+    return maildir.add(msg)
+
+
+class TestGetRecentKeys:
+    def test_recent_file_selected(self, tmp_path):
+        md = make_maildir(tmp_path)
+        msg = build_email()
+        md.add(msg)
+        md.flush()
+        # mtime is now → within the window
+        keys = get_recent_keys(md, days=7)
+        assert len(keys) == 1
+
+    def test_old_file_excluded(self, tmp_path):
+        md = make_maildir(tmp_path)
+        md.add(build_email())
+        md.flush()
+        # Age every file beyond the cutoff
+        old = time.time() - 30 * 86400
+        for path in tmp_path.rglob("*.??*"):
+            if path.is_file():
+                os.utime(path, (old, old))
+        keys = get_recent_keys(md, days=7)
+        assert len(keys) == 0
+
+    def test_key_is_suffixless_filename(self, tmp_path):
+        """Maildir keys strip the ':2,S' info suffix — get_recent_keys must match."""
+        md = make_maildir(tmp_path)
+        key = md.add(build_email())
+        md.flush()
+        keys = get_recent_keys(md, days=7)
+        assert keys  # non-empty set of keys for fresh files
+        assert key.split(":")[0] in keys
+        for k in keys:
+            assert ":" not in k
diff --git a/tests/test_integration.py b/tests/test_integration.py
index dd53c7f..c74251b 100644
--- a/tests/test_integration.py
+++ b/tests/test_integration.py
@@ -1,16 +1,21 @@
-"""Integration tests for mcp-maildir with a real Qdrant instance."""
+"""Integration tests for mcp-maildir with a real Qdrant instance.
+
+Env vars (QDRANT_URL, COLLECTION_NAME, EMBEDDING_MODEL_NAME) are set in
+tests/conftest.py — don't set them here, they must match server.py's
+import-time snapshot for every module in the session.
+"""
 
 import os
 import uuid
 import pytest
 
-os.environ["QDRANT_URL"] = "http://localhost:6333"
-os.environ["COLLECTION_NAME"] = "test_mcp_maildir"
-os.environ["EMBEDDING_MODEL_NAME"] = "BAAI/bge-small-en-v1.5"
-
 from server import get_qdrant_client, get_embedding_model, search_emails, read_email
 from qdrant_client.http import models
 
+# Requires a live Qdrant on localhost:6333 (see pytest.ini: deselected by
+# default; run with `pytest -m integration`, nightly CI does exactly that).
+pytestmark = pytest.mark.integration
+
 
 TEST_EMAILS = [
     {
@@ -56,6 +61,21 @@ def qdrant_setup():
     model = get_embedding_model()
     collection_name = os.environ["COLLECTION_NAME"]
 
+    # Debug instrumentalisation — truth about which server we are talking to
+    # and what it holds (CI 404 diagnosis).
+    import logging
+    dbg = logging.getLogger("integration.debug")
+    try:
+        dbg.warning("qdrant client url: %s", client.http._client.base_url)
+    except Exception:
+        dbg.warning("qdrant client url: <introspection failed>")
+    server_info = None
+    try:
+        server_info = client.get_collections()
+        dbg.warning("collections BEFORE: %s", [c.name for c in server_info.collections])
+    except Exception as e:
+        dbg.warning("get_collections FAILED: %s", e)
+
     # Clean up from previous runs
     try:
         client.delete_collection(collection_name)
@@ -70,6 +90,14 @@ def qdrant_setup():
             size=len(probe), distance=models.Distance.COSINE
         ),
     )
+    # Assert the collection is actually visible right after creation
+    names_after = [c.name for c in client.get_collections().collections]
+    dbg.warning("collections AFTER create: %s", names_after)
+    if collection_name not in names_after:
+        raise RuntimeError(
+            f"Fixture created collection {collection_name} but it is not in "
+            f"get_collections(): {names_after}"
+        )
 
     # Index test emails
     for email in TEST_EMAILS:
diff --git a/tests/test_server.py b/tests/test_server.py
index a4c71d8..34ad7db 100644
--- a/tests/test_server.py
+++ b/tests/test_server.py
@@ -1,13 +1,14 @@
-"""Unit tests for mcp-maildir server pure functions."""
+"""Unit tests for mcp-maildir server pure functions.
 
-import os
-os.environ["QDRANT_URL"] = "http://localhost:6333"
-os.environ["COLLECTION_NAME"] = "test"
+Env vars are set in tests/conftest.py (shared session-wide) — see the
+conftest docstring for why test modules must not touch os.environ.
+"""
 
 from server import (
     normalize_email_address,
     payload_matches_participant,
     format_search_result,
+    build_filter,
 )
 
 
@@ -108,3 +109,55 @@ class TestFormatSearchResult:
         assert result["receiver"] is None
         assert result["subject"] is None
         assert result["attachments"] == []
+
+
+class TestBuildFilter:
+    def test_no_filters_returns_none(self):
+        assert build_filter(None, None, None) is None
+
+    def test_empty_strings_return_none(self):
+        assert build_filter("", "", "") is None
+
+    def test_participant_filter_is_should_clause_on_sender_and_receiver(self):
+        f = build_filter("alice@example.com", None, None)
+        assert f is not None
+        # The date conditions list must be absent and only the participant filter present
+        assert len(f.must) == 1
+        participant = f.must[0]
+        keys = [c.key for c in participant.should]
+        assert keys == ["sender", "receiver"]
+        assert all(c.match.value == "alice@example.com" for c in participant.should)
+
+    def test_participant_normalized_before_match(self):
+        f = build_filter("Alice <Alice@Example.COM>", None, None)
+        should = f.must[0].should
+        assert all(c.match.value == "alice@example.com" for c in should)
+
+    def test_date_range_only(self):
+        f = build_filter(None, "2026-01-01", "2026-06-30")
+        assert len(f.must) == 1
+        cond = f.must[0]
+        assert cond.key == "date"
+        assert cond.range.gte is not None
+        assert cond.range.lte is not None
+
+    def test_start_date_only(self):
+        f = build_filter(None, "2026-03-15", None)
+        cond = f.must[0]
+        assert cond.range.gte is not None
+        assert cond.range.lte is None
+
+    def test_end_date_only(self):
+        f = build_filter(None, None, "2026-03-15")
+        cond = f.must[0]
+        assert cond.range.gte is None
+        assert cond.range.lte is not None
+
+    def test_combined_participant_and_date(self):
+        f = build_filter("bob@example.org", "2026-01-01", "2026-12-31")
+        assert len(f.must) == 2
+        # One is the participant should-filter, the other the date range
+        kinds = sorted(
+            "participant" if getattr(c, "should", None) else "date" for c in f.must
+        )
+        assert kinds == ["date", "participant"]