diff --git a/cmd/dmarc-report-converter/output_test.go b/cmd/dmarc-report-converter/output_test.go
new file mode 100644
index 0000000..66cb5c4
--- /dev/null
+++ b/cmd/dmarc-report-converter/output_test.go
@@ -0,0 +1,158 @@
+package main
+
+import (
+	"bytes"
+	"html/template"
+	"testing"
+	"time"
+
+	"github.com/tierpod/dmarc-report-converter/pkg/dmarc"
+)
+
+func TestExternalTemplate(t *testing.T) {
+	r := `<?xml version="1.0"?>
+<feedback>
+  <report_metadata>
+    <org_name>Org 1</org_name>
+    <email>foo@bar.baz</email>
+    <report_id>1712279633.907274</report_id>
+    <date_range>
+      <begin>1712188800</begin>
+      <end>1712275199</end>
+    </date_range>
+  </report_metadata>
+  <policy_published>
+    <domain>report.test</domain>
+    <adkim>r</adkim>
+    <aspf>r</aspf>
+    <p>none</p>
+    <pct>100</pct>
+  </policy_published>
+  <record>
+    <row>
+      <source_ip>1.2.3.4</source_ip>
+      <count>1</count>
+      <policy_evaluated>
+        <disposition>none</disposition>
+        <dkim>pass</dkim>
+        <spf>fail</spf>
+      </policy_evaluated>
+    </row>
+    <identifiers>
+      <header_from>headerfrom.test</header_from>
+    </identifiers>
+    <auth_results>
+      <dkim>
+        <domain>auth.test</domain>
+        <selector>1000073432</selector>
+        <result>pass</result>
+      </dkim>
+      <dkim>
+        <domain>cust.test</domain>
+        <selector>2020263919</selector>
+        <result>pass</result>
+      </dkim>
+      <spf>
+        <domain>spf.test</domain>
+        <result>pass</result>
+      </spf>
+    </auth_results>
+  </record>
+</feedback>
+`
+
+	tests := map[string]struct {
+		tmpl   string
+		expect string
+	}{
+		".AssetsPath": {
+			`{{ .AssetsPath }}`,
+			`/foo`,
+		},
+		".Report.XMLName.Local": {
+			`{{ .Report.XMLName.Local }}`,
+			`feedback`,
+		},
+		".Report.ReportMetadata": {
+			`{{ .Report.ReportMetadata }}`,
+			`{Org 1 foo@bar.baz  1712279633.907274 {2024-04-04 00:00:00 &#43;0000 UTC 2024-04-04 23:59:59 &#43;0000 UTC}}`,
+		},
+		".Report.PolicyPublished": {
+			`{{ .Report.PolicyPublished }}`,
+			`{report.test r r none  100}`,
+		},
+		".Report.Records": {
+			"{{ range .Report.Records }}\n- {{ . }}\n{{ end -}}",
+			"\n- {{1.2.3.4 1 {none pass fail} } {headerfrom.test } {[{auth.test pass 1000073432} {cust.test pass 2020263919}] [{spf.test pass }]}}\n",
+		},
+		".Report.MessagesStats": {
+			`{{ .Report.MessagesStats }}`,
+			`{1 0 1 100}`,
+		},
+
+		// Deprecated
+		".XMLName.Local": {
+			`{{ .XMLName.Local }}`,
+			`feedback`,
+		},
+		".ReportMetadata": {
+			`{{ .ReportMetadata }}`,
+			`{Org 1 foo@bar.baz  1712279633.907274 {2024-04-04 00:00:00 &#43;0000 UTC 2024-04-04 23:59:59 &#43;0000 UTC}}`,
+		},
+		".PolicyPublished": {
+			`{{ .PolicyPublished }}`,
+			`{report.test r r none  100}`,
+		},
+		".MessagesStats": {
+			`{{ .MessagesStats }}`,
+			`{1 0 1 100}`,
+		},
+	}
+
+	// Set the timezone so that timestamps match regardless of local system time
+	origLocal := time.Local
+
+	loc, err := time.LoadLocation("UTC")
+	if err != nil {
+		t.Errorf("unable to load UTC timezone: %s", err)
+	}
+	time.Local = loc
+	defer func() {
+		// Reset timezone
+		time.Local = origLocal
+	}()
+
+	report, err := dmarc.Parse([]byte(r), false, 1)
+	if err != nil {
+		t.Fatalf("unexpected error parsing XML: %s", err)
+	}
+
+	for name, test := range tests {
+		conf := config{
+			Output: Output{
+				AssetsPath: "/foo",
+				template: template.Must(template.New("report").Funcs(
+					template.FuncMap{
+						"now": func(fmt string) string {
+							return time.Now().Format(fmt)
+						},
+					},
+				).Parse(test.tmpl)),
+			},
+		}
+
+		var buf bytes.Buffer
+		out := newOutput(&conf)
+		out.w = &buf
+
+		err = out.template(report)
+		if err != nil {
+			t.Fatalf("%s: unexpected error building template: %s", name, err)
+		}
+
+		if buf.String() != test.expect {
+			t.Errorf("%s\nWANT:\n%s\nGOT:\n%s", name, test.expect, buf.String())
+		}
+
+	}
+}