diff --git a/Dockerfile b/Dockerfile
index a807981..0b941cd 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -43,7 +43,7 @@ RUN set -eux; \
   cargo --version
 
 ENV DATA_DIR=/var/lib/rustbox-package-builder \
-  CARGO_TARGET_DIR=/var/lib/rustbox-package-builder/cargo/target
+  CARGO_TARGET_DIR=/tmp/rustbox-package-builder/cargo-target
 
 COPY scripts/ /opt/rustbox-package-builder/scripts/
 COPY packaging/ /opt/rustbox-package-builder/packaging/
diff --git a/README.md b/README.md
index a7af650..7eb49eb 100644
--- a/README.md
+++ b/README.md
@@ -72,10 +72,18 @@ PACKAGE_RELEASE=auto
 RUN_LINUX_TESTS=compile
 MAX_GLIBC_VERSION=2.34
 RELEASE_RETENTION=10
+PACKAGE_RETENTION=10
+CLEAN_BUILD_CACHE=1
 ```
 
 `RUN_LINUX_TESTS=compile` runs `cargo test --release --locked --no-run`. Use `full` to run the test suite or `0` to skip Rust tests.
 
+`PACKAGE_RETENTION=10` keeps at most the 10 newest DEB packages, 10 newest RHEL-family RPM packages, and 10 newest SUSE RPM packages in the published package pools. `RELEASE_RETENTION=10` separately controls atomic repository release directories.
+
+`CLEAN_BUILD_CACHE=1` removes the Cargo target directory after every build (successful or failed). Build output and package staging directories always live under `/tmp/rustbox-package-builder` and are removed after each build, so repeated compilations do not accumulate large compiler artifacts in `data/`. Set `CLEAN_BUILD_CACHE=0` only if you deliberately want to trade disk space for faster subsequent builds.
+
+On startup the builder also removes legacy `data/cargo/target`, `data/work/out`, and `data/work/package` directories created by older releases.
+
 All three supported Linux package families are built on every successful release. SUSE is not treated as a separate non-Linux target.
 
 ## Installed RustBox layout
diff --git a/docker-compose.yml b/docker-compose.yml
index ff416f3..55b6caa 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -14,6 +14,8 @@ services:
       RUN_LINUX_TESTS: "${RUN_LINUX_TESTS:-compile}"
       MAX_GLIBC_VERSION: "${MAX_GLIBC_VERSION:-2.34}"
       RELEASE_RETENTION: "${RELEASE_RETENTION:-10}"
+      PACKAGE_RETENTION: "${PACKAGE_RETENTION:-10}"
+      CLEAN_BUILD_CACHE: "${CLEAN_BUILD_CACHE:-1}"
     volumes:
       - ./data:/var/lib/rustbox-package-builder
       - ./gpg:/run/secrets/gpg:ro
diff --git a/packaging/rustbox.toml b/packaging/rustbox.toml
index 1f374e5..69e3480 100644
--- a/packaging/rustbox.toml
+++ b/packaging/rustbox.toml
@@ -39,6 +39,12 @@ default_interface_skin = "apple-mail"
 sieve_enabled = true
 diagnostics_enabled = true
 about_enabled = true
+
+# Allow multiple IMAP accounts in one browser session.
+# When disabled, RustBox hides multi-account UI, rejects adding another account,
+# and realtime notifications/watchers are limited to the active account.
+multi_account_enabled = true
+
 # Security headers added by RustBox. Off by default for compatibility.
 #
 # When enabled:
diff --git a/scripts/build-release.sh b/scripts/build-release.sh
index e586241..0823d60 100755
--- a/scripts/build-release.sh
+++ b/scripts/build-release.sh
@@ -5,10 +5,21 @@ source /opt/rustbox-package-builder/scripts/lib.sh
 : "${SRC:?SRC required}"
 REPOSITORY="$DATA_DIR/repository"
 APTLY_CONF="$DATA_DIR/state/aptly.conf"
-OUT="$DATA_DIR/work/out"
-PKG="$DATA_DIR/work/package"
-rm -rf "$OUT" "$PKG"
-mkdir -p "$OUT" "$DATA_DIR/packages/deb" "$DATA_DIR/packages/rpm/x86_64" "$DATA_DIR/packages/suse/x86_64"
+BUILD_TMP_DIR=${BUILD_TMP_DIR:-/tmp/rustbox-package-builder}
+OUT="$BUILD_TMP_DIR/out"
+PKG="$BUILD_TMP_DIR/package"
+export CARGO_TARGET_DIR=${CARGO_TARGET_DIR:-$BUILD_TMP_DIR/cargo-target}
+
+cleanup_build_artifacts() {
+  rm -rf -- "$OUT" "$PKG"
+  if is_true "${CLEAN_BUILD_CACHE:-1}"; then
+    rm -rf -- "$CARGO_TARGET_DIR"
+  fi
+}
+trap cleanup_build_artifacts EXIT
+
+rm -rf -- "$OUT" "$PKG"
+mkdir -p "$OUT" "$DATA_DIR/packages/deb" "$DATA_DIR/packages/rpm/x86_64" "$DATA_DIR/packages/suse/x86_64" "$CARGO_TARGET_DIR"
 
 VERSION=$(python3.11 - "$SRC/Cargo.toml" <<'PY'
 import sys, tomllib
@@ -78,7 +89,16 @@ cp -f "$DEB" "$DATA_DIR/packages/deb/"
 cp -f "$RPM" "$DATA_DIR/packages/rpm/x86_64/"
 cp -f "$SUSE" "$DATA_DIR/packages/suse/x86_64/"
 
-aptly -config="$APTLY_CONF" repo add -force-replace rustbox "$DEB" >/dev/null
+package_retention=${PACKAGE_RETENTION:-10}
+prune_package_files "$DATA_DIR/packages/deb" 'rustbox_*.deb' "$package_retention"
+prune_package_files "$DATA_DIR/packages/rpm/x86_64" 'rustbox-*.x86_64.rpm' "$package_retention"
+prune_package_files "$DATA_DIR/packages/suse/x86_64" 'rustbox-*.suse.x86_64.rpm' "$package_retention"
+
+# Keep the mutable aptly repository in exact sync with the retained DEB files.
+# Published snapshots are immutable, so rebuilding this repo does not disturb the
+# currently served repository until the new snapshot is switched in below.
+aptly -config="$APTLY_CONF" repo remove rustbox rustbox >/dev/null 2>&1 || true
+aptly -config="$APTLY_CONF" repo add -force-replace rustbox "$DATA_DIR/packages/deb" >/dev/null
 SNAPSHOT="rustbox-${VERSION}-${SHORT_SHA}-$(date +%s)"
 aptly -config="$APTLY_CONF" snapshot create "$SNAPSHOT" from repo rustbox >/dev/null
 APT_SIGN=(-batch -gpg-key="$GPG_KEY_ID")
@@ -90,12 +110,28 @@ fi
 APT_PUBLIC="$DATA_DIR/aptly/public"
 [[ -f "$APT_PUBLIC/dists/$REPO_DISTRIBUTION/InRelease" ]] || fatal "APT InRelease missing"
 
+# Once the new snapshot is live, old aptly snapshots no longer serve traffic.
+# Drop them and let aptly remove unreferenced pool objects.
+while IFS= read -r old_snapshot; do
+  [[ -n "$old_snapshot" && "$old_snapshot" != "$SNAPSHOT" ]] || continue
+  if ! aptly -config="$APTLY_CONF" snapshot drop "$old_snapshot" >/dev/null 2>&1; then
+    log "WARN: could not drop old aptly snapshot $old_snapshot"
+  fi
+done < <(aptly -config="$APTLY_CONF" snapshot list -raw | grep '^rustbox-' || true)
+if ! aptly -config="$APTLY_CONF" db cleanup >/dev/null 2>&1; then
+  log "WARN: aptly database cleanup failed"
+fi
+
 RELEASE_ID="$(date -u '+%Y%m%dT%H%M%SZ')-${SHORT_SHA}"
 RELEASE_DIR="$REPOSITORY/releases/$RELEASE_ID"
 mkdir -p "$RELEASE_DIR/apt" "$RELEASE_DIR/rpm/x86_64" "$RELEASE_DIR/suse/x86_64"
-rsync -a --delete "$APT_PUBLIC/" "$RELEASE_DIR/apt/"
-rsync -a --delete "$DATA_DIR/packages/rpm/x86_64/" "$RELEASE_DIR/rpm/x86_64/"
-rsync -a --delete "$DATA_DIR/packages/suse/x86_64/" "$RELEASE_DIR/suse/x86_64/"
+
+# All paths are on the same persistent data volume. Hard-linking package and
+# repository files avoids multiplying identical package payloads for every
+# atomic release directory while preserving independent directory trees.
+cp -al "$APT_PUBLIC/." "$RELEASE_DIR/apt/"
+cp -al "$DATA_DIR/packages/rpm/x86_64/." "$RELEASE_DIR/rpm/x86_64/"
+cp -al "$DATA_DIR/packages/suse/x86_64/." "$RELEASE_DIR/suse/x86_64/"
 
 for rpm_root in "$RELEASE_DIR/rpm/x86_64"; do
   rm -rf "$rpm_root/repodata"; createrepo_c --update "$rpm_root" >/dev/null
@@ -135,9 +171,6 @@ printf '%s\n' "$SHA" | atomic_write "$DATA_DIR/state/last_commit"
 printf '%s\n' "$VERSION" | atomic_write "$DATA_DIR/state/last_version"
 printf '%s\n' "$RELEASE" | atomic_write "$DATA_DIR/state/last_package_release"
 
-retention=${RELEASE_RETENTION:-10}
-if [[ "$retention" =~ ^[1-9][0-9]*$ ]]; then
-  mapfile -t old < <(find "$REPOSITORY/releases" -mindepth 1 -maxdepth 1 -type d -printf '%T@ %p\n' | sort -nr | awk -v keep="$retention" 'NR>keep {$1=""; sub(/^ /,""); print}')
-  for dir in "${old[@]}"; do [[ "$dir" == "$RELEASE_DIR" ]] || rm -rf -- "$dir"; done
-fi
+release_retention=${RELEASE_RETENTION:-10}
+prune_release_dirs "$REPOSITORY/releases" "$release_retention" "$RELEASE_DIR"
 log "published RustBox $VERSION-$RELEASE: $REPOSITORY_URL"
diff --git a/scripts/entrypoint.sh b/scripts/entrypoint.sh
index e46cd58..374c999 100755
--- a/scripts/entrypoint.sh
+++ b/scripts/entrypoint.sh
@@ -11,9 +11,31 @@ source /opt/rustbox-package-builder/scripts/lib.sh
 : "${RUN_LINUX_TESTS:=compile}"
 : "${MAX_GLIBC_VERSION:=2.34}"
 : "${RELEASE_RETENTION:=10}"
-export SOURCE_BRANCH POLL_INTERVAL REPO_DISTRIBUTION REPO_COMPONENT PACKAGE_RELEASE RUN_LINUX_TESTS MAX_GLIBC_VERSION RELEASE_RETENTION
-mkdir -p "$DATA_DIR"/{state,repository,work,cargo,packages} /tmp/rustbox-gnupg
+: "${PACKAGE_RETENTION:=10}"
+: "${CLEAN_BUILD_CACHE:=1}"
+: "${BUILD_TMP_DIR:=/tmp/rustbox-package-builder}"
+require_positive_integer RELEASE_RETENTION "$RELEASE_RETENTION"
+require_positive_integer PACKAGE_RETENTION "$PACKAGE_RETENTION"
+export SOURCE_BRANCH POLL_INTERVAL REPO_DISTRIBUTION REPO_COMPONENT PACKAGE_RELEASE RUN_LINUX_TESTS MAX_GLIBC_VERSION RELEASE_RETENTION PACKAGE_RETENTION CLEAN_BUILD_CACHE BUILD_TMP_DIR
+mkdir -p "$DATA_DIR"/{state,repository,work,packages} "$BUILD_TMP_DIR" /tmp/rustbox-gnupg
 chmod 0700 /tmp/rustbox-gnupg
+
+# Migration/maintenance cleanup for older builder versions which stored large
+# cargo targets and package work directories on the persistent data volume.
+rm -rf -- "$DATA_DIR/work/out" "$DATA_DIR/work/package" "$DATA_DIR/cargo/target"
+rmdir "$DATA_DIR/cargo" 2>/dev/null || true
+rm -rf -- "$BUILD_TMP_DIR/out" "$BUILD_TMP_DIR/package"
+if is_true "$CLEAN_BUILD_CACHE"; then
+  rm -rf -- "$BUILD_TMP_DIR/cargo-target"
+fi
+
+# Apply file-level retention at startup as well, so stale raw package pools and
+# old atomic release directories are reduced even before the next source build.
+prune_package_files "$DATA_DIR/packages/deb" 'rustbox_*.deb' "$PACKAGE_RETENTION"
+prune_package_files "$DATA_DIR/packages/rpm/x86_64" 'rustbox-*.x86_64.rpm' "$PACKAGE_RETENTION"
+prune_package_files "$DATA_DIR/packages/suse/x86_64" 'rustbox-*.suse.x86_64.rpm' "$PACKAGE_RETENTION"
+prune_release_dirs "$DATA_DIR/repository/releases" "$RELEASE_RETENTION" "$(readlink -f "$DATA_DIR/repository/current" 2>/dev/null || true)"
+
 export GNUPGHOME=/tmp/rustbox-gnupg
 GPG_PRIVATE_KEY_FILE=/run/secrets/gpg/private-key.asc
 [[ -s "$GPG_PRIVATE_KEY_FILE" ]] || fatal "missing GPG private key: $GPG_PRIVATE_KEY_FILE"
diff --git a/scripts/lib.sh b/scripts/lib.sh
index 6cdfdce..38632fb 100755
--- a/scripts/lib.sh
+++ b/scripts/lib.sh
@@ -1,7 +1,7 @@
 #!/usr/bin/env bash
 set -Eeuo pipefail
 
-PACKAGING_REVISION=2
+PACKAGING_REVISION=3
 DATA_DIR=${DATA_DIR:-/var/lib/rustbox-package-builder}
 
 log() { printf '%s %s\n' "$(date -u '+%Y-%m-%dT%H:%M:%SZ')" "$*"; }
@@ -13,3 +13,53 @@ print(json.dumps(sys.argv[1]))
 PY
 }
 atomic_write() { local path=$1 tmp="${path}.tmp.$$"; cat > "$tmp"; mv -f "$tmp" "$path"; }
+
+is_true() {
+  case "${1:-}" in
+    1|true|TRUE|yes|YES|on|ON) return 0 ;;
+    *) return 1 ;;
+  esac
+}
+
+require_positive_integer() {
+  local name=$1 value=$2
+  [[ "$value" =~ ^[1-9][0-9]*$ ]] || fatal "$name must be a positive integer"
+}
+
+prune_package_files() {
+  local directory=$1 pattern=$2 keep=$3
+  require_positive_integer PACKAGE_RETENTION "$keep"
+  [[ -d "$directory" ]] || return 0
+
+  mapfile -t stale < <(
+    find "$directory" -maxdepth 1 -type f -name "$pattern" -printf '%T@ %p\n' \
+      | sort -nr \
+      | awk -v keep="$keep" 'NR>keep {$1=""; sub(/^ /,""); print}'
+  )
+
+  local path
+  for path in "${stale[@]}"; do
+    [[ -n "$path" ]] || continue
+    log "package retention: removing $path"
+    rm -f -- "$path"
+  done
+}
+
+prune_release_dirs() {
+  local releases_dir=$1 keep=$2 protected=${3:-}
+  require_positive_integer RELEASE_RETENTION "$keep"
+  [[ -d "$releases_dir" ]] || return 0
+
+  mapfile -t stale < <(
+    find "$releases_dir" -mindepth 1 -maxdepth 1 -type d -printf '%T@ %p\n' \
+      | sort -nr \
+      | awk -v keep="$keep" 'NR>keep {$1=""; sub(/^ /,""); print}'
+  )
+
+  local path
+  for path in "${stale[@]}"; do
+    [[ -n "$path" && "$path" != "$protected" ]] || continue
+    log "release retention: removing $path"
+    rm -rf -- "$path"
+  done
+}
diff --git a/start.sh b/start.sh
index eba2e52..e84994f 100755
--- a/start.sh
+++ b/start.sh
@@ -53,7 +53,7 @@ if [[ "$REPOSITORY_URL" == http://* && ! "$REPOSITORY_URL" =~ :[0-9]+$ ]]; then
   log "REPOSITORY_URL updated to $REPOSITORY_URL"
 fi
 
-mkdir -p "$DATA_DIR"/{repository,state,cargo,work,packages} "$GPG_DIR"
+mkdir -p "$DATA_DIR"/{repository,state,work,packages} "$GPG_DIR"
 chmod 0700 "$GPG_DIR" 2>/dev/null || true
 
 log "building builder and repository dashboard"
diff --git a/tests/test_packaging.py b/tests/test_packaging.py
index 9544271..942285a 100644
--- a/tests/test_packaging.py
+++ b/tests/test_packaging.py
@@ -1,4 +1,7 @@
 from pathlib import Path
+import os
+import subprocess
+import tempfile
 import tomllib
 
 ROOT = Path(__file__).resolve().parents[1]
@@ -85,4 +88,47 @@ def test_rustup_installation_and_runtime_cargo_home_are_consistent():
     assert "CARGO_HOME=/opt/cargo" in dockerfile
     runtime_env = dockerfile.split("ENV DATA_DIR=/var/lib/rustbox-package-builder", 1)[1]
     assert "CARGO_HOME=/var/lib/rustbox-package-builder/cargo" not in runtime_env
-    assert "CARGO_TARGET_DIR=/var/lib/rustbox-package-builder/cargo/target" in runtime_env
+    assert "CARGO_TARGET_DIR=/tmp/rustbox-package-builder/cargo-target" in runtime_env
+    assert "CARGO_TARGET_DIR=/var/lib/rustbox-package-builder/cargo/target" not in runtime_env
+
+
+
+def test_build_cache_cleanup_and_package_retention_defaults():
+    env = (ROOT / ".env.example").read_text()
+    compose = (ROOT / "docker-compose.yml").read_text()
+    entrypoint = (ROOT / "scripts/entrypoint.sh").read_text()
+    build = (ROOT / "scripts/build-release.sh").read_text()
+
+    assert "PACKAGE_RETENTION=10" in env
+    assert "CLEAN_BUILD_CACHE=1" in env
+    assert 'PACKAGE_RETENTION: "${PACKAGE_RETENTION:-10}"' in compose
+    assert 'CLEAN_BUILD_CACHE: "${CLEAN_BUILD_CACHE:-1}"' in compose
+    assert 'rm -rf -- "$DATA_DIR/work/out" "$DATA_DIR/work/package" "$DATA_DIR/cargo/target"' in entrypoint
+    assert 'trap cleanup_build_artifacts EXIT' in build
+    assert 'aptly -config="$APTLY_CONF" db cleanup' in build
+    assert 'cp -al "$DATA_DIR/packages/rpm/x86_64/." "$RELEASE_DIR/rpm/x86_64/"' in build
+
+
+def test_prune_package_files_keeps_only_newest_ten():
+    with tempfile.TemporaryDirectory() as tmp:
+        root = Path(tmp)
+        pkg = root / "deb"
+        pkg.mkdir()
+        for idx in range(12):
+            path = pkg / f"rustbox_0.2.{idx}-1_amd64.deb"
+            path.write_bytes(str(idx).encode())
+            ts = 1_700_000_000 + idx
+            os.utime(path, (ts, ts))
+
+        script = "\n".join([
+            "set -Eeuo pipefail",
+            f"source {ROOT / 'scripts/lib.sh'}",
+            f"prune_package_files {pkg} 'rustbox_*.deb' 10",
+        ])
+        subprocess.run(["bash", "-lc", script], check=True)
+
+        remaining = sorted(p.name for p in pkg.glob("*.deb"))
+        assert len(remaining) == 10
+        assert "rustbox_0.2.0-1_amd64.deb" not in remaining
+        assert "rustbox_0.2.1-1_amd64.deb" not in remaining
+        assert "rustbox_0.2.11-1_amd64.deb" in remaining