diff --git a/modules/services/lieer.nix b/modules/services/lieer.nix
index 571e2af7..eb419840 100644
--- a/modules/services/lieer.nix
+++ b/modules/services/lieer.nix
@@ -26,6 +26,8 @@ let
         Type = "oneshot";
         ExecStart = "${pkgs.gmailieer}/bin/gmi sync";
         WorkingDirectory = account.maildir.absPath;
+        Environment = mkIf (config.home.sessionVariables ? NOTMUCH_CONFIG)
+          "NOTMUCH_CONFIG=${config.home.sessionVariables.NOTMUCH_CONFIG}";
       };
     };
   };
diff --git a/tests/modules/services/lieer/lieer-service.nix b/tests/modules/services/lieer/account-with-notmuch.nix
similarity index 55%
rename from tests/modules/services/lieer/lieer-service.nix
rename to tests/modules/services/lieer/account-with-notmuch.nix
index af3074b0..b6c85384 100644
--- a/tests/modules/services/lieer/lieer-service.nix
+++ b/tests/modules/services/lieer/account-with-notmuch.nix
@@ -6,6 +6,7 @@ with lib;
   imports = [ ../../accounts/email-test-accounts.nix ];
 
   config = {
+    programs.notmuch.enable = true;
     services.lieer.enable = true;
 
     accounts.email.accounts = {
@@ -24,6 +25,8 @@ with lib;
         gmailieer = pkgs.writeScriptBin "dummy-gmailieer" "" // {
           outPath = "@lieer@";
         };
+
+        notmuch = pkgs.writeScriptBin "dummy-notmuch" "";
       })
     ];
 
@@ -32,7 +35,19 @@ with lib;
       assertFileExists home-files/.config/systemd/user/lieer-hm-example-com.timer
 
       assertFileContent home-files/.config/systemd/user/lieer-hm-example-com.service \
-                        ${./lieer-service-expected.service}
+                        ${
+                          pkgs.writeText "lieer-service-expected.service" ''
+                            [Service]
+                            Environment=NOTMUCH_CONFIG=/home/hm-user/.config/notmuch/notmuchrc
+                            ExecStart=@lieer@/bin/gmi sync
+                            Type=oneshot
+                            WorkingDirectory=/home/hm-user/Mail/hm@example.com
+
+                            [Unit]
+                            ConditionPathExists=/home/hm-user/Mail/hm@example.com/.gmailieer.json
+                            Description=lieer Gmail synchronization for hm@example.com
+                          ''
+                        }
       assertFileContent home-files/.config/systemd/user/lieer-hm-example-com.timer \
                         ${./lieer-service-expected.timer}
     '';
diff --git a/tests/modules/services/lieer/account-without-notmuch.nix b/tests/modules/services/lieer/account-without-notmuch.nix
new file mode 100644
index 00000000..e2039551
--- /dev/null
+++ b/tests/modules/services/lieer/account-without-notmuch.nix
@@ -0,0 +1,60 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+{
+  imports = [ ../../accounts/email-test-accounts.nix ];
+
+  config = {
+    services.lieer.enable = true;
+
+    accounts.email.accounts = {
+      "hm@example.com".lieer.enable = true;
+      "hm@example.com".lieer.sync.enable = true;
+    };
+
+    nixpkgs.overlays = [
+      (self: super: {
+        gmailieer = pkgs.writeScriptBin "dummy-gmailieer" "" // {
+          outPath = "@lieer@";
+        };
+      })
+    ];
+
+    test.asserts.warnings.expected = [''
+      lieer is enabled for the following email accounts, but notmuch is not:
+
+          hm@example.com
+
+      Notmuch can be enabled with:
+
+          accounts.email.accounts.hm@example.com.notmuch.enable = true;
+
+      If you have configured notmuch outside of Home Manager, you can suppress this
+      warning with:
+
+          programs.lieer.notmuchSetupWarning = false;
+    ''];
+
+    nmt.script = ''
+      assertFileExists home-files/.config/systemd/user/lieer-hm-example-com.service
+      assertFileExists home-files/.config/systemd/user/lieer-hm-example-com.timer
+
+      assertFileContent home-files/.config/systemd/user/lieer-hm-example-com.service \
+                        ${
+                          pkgs.writeText "lieer-service-expected.service" ''
+                            [Service]
+                            ExecStart=@lieer@/bin/gmi sync
+                            Type=oneshot
+                            WorkingDirectory=/home/hm-user/Mail/hm@example.com
+
+                            [Unit]
+                            ConditionPathExists=/home/hm-user/Mail/hm@example.com/.gmailieer.json
+                            Description=lieer Gmail synchronization for hm@example.com
+                          ''
+                        }
+      assertFileContent home-files/.config/systemd/user/lieer-hm-example-com.timer \
+                        ${./lieer-service-expected.timer}
+    '';
+  };
+}
diff --git a/tests/modules/services/lieer/default.nix b/tests/modules/services/lieer/default.nix
index 1d6b435a..864c5f2e 100644
--- a/tests/modules/services/lieer/default.nix
+++ b/tests/modules/services/lieer/default.nix
@@ -1 +1,4 @@
-{ lieer-service = ./lieer-service.nix; }
+{
+  lieer-account-with-notmuch = ./account-with-notmuch.nix;
+  lieer-account-without-notmuch = ./account-without-notmuch.nix;
+}
diff --git a/tests/modules/services/lieer/lieer-service-expected.service b/tests/modules/services/lieer/lieer-service-expected.service
deleted file mode 100644
index 1110e85c..00000000
--- a/tests/modules/services/lieer/lieer-service-expected.service
+++ /dev/null
@@ -1,8 +0,0 @@
-[Service]
-ExecStart=@lieer@/bin/gmi sync
-Type=oneshot
-WorkingDirectory=/home/hm-user/Mail/hm@example.com
-
-[Unit]
-ConditionPathExists=/home/hm-user/Mail/hm@example.com/.gmailieer.json
-Description=lieer Gmail synchronization for hm@example.com