diff --git a/app/assets/javascripts/app/lib/app_post/utils.coffee b/app/assets/javascripts/app/lib/app_post/utils.coffee
index 3d506bed1..39b8105d8 100644
--- a/app/assets/javascripts/app/lib/app_post/utils.coffee
+++ b/app/assets/javascripts/app/lib/app_post/utils.coffee
@@ -795,8 +795,8 @@ class App.Utils
     try content = $('<div/>').html(message)
     catch e then content = $('<div/>').html('<div>' + message + '</div>')
 
-    # ignore mail structures of case Ticket#1085048
-    return message if content.find("div:first span:contains('CAUTION:')").css('color') == 'rgb(156, 101, 0)'
+    # Invalid html signature detection for exchange warning boxes #3571
+    return message if content.find("div:first:contains('CAUTION:')").length > 0
 
     content.contents().each (index, node) ->
       text = $(node).text()
diff --git a/lib/signature_detection.rb b/lib/signature_detection.rb
index 2bb62e40c..82d1d530b 100644
--- a/lib/signature_detection.rb
+++ b/lib/signature_detection.rb
@@ -47,6 +47,9 @@ returns
                         .map { |l| l.sub(%r{^.}, '') }
                         .first(10).join("\n")
 
+      # Invalid html signature detection for exchange warning boxes #3571
+      next if match_content.include?('CAUTION:')
+
       # Add this substring to the signature_candidates hash and increment its match score
       signature_candidates[match_content] += 1
     end
diff --git a/public/assets/tests/html_utils.js b/public/assets/tests/html_utils.js
index c44b0c9d2..c45278a76 100644
--- a/public/assets/tests/html_utils.js
+++ b/public/assets/tests/html_utils.js
@@ -1083,12 +1083,18 @@ test("identify signature by HTML", function() {
   result  = App.Utils.signatureIdentifyByHtml(message)
   equal(result, should)
 
-  // ignore mail structures of case Ticket#1085048
+  // Invalid html signature detection for exchange warning boxes #3571
   message = '<div><span style="color:#9c6500;">CAUTION:</span> This email originated from outside of the organization. Do not click links or open attachments unless you recognize the sender and know the content is safe.</div><br><div><p>actual content</p><div><p>actual content 2</p></div><p>&nbsp;</p><div><p>actual quote</p></div><div><blockquote><p>actual quote</p></blockquote></div><div><p>&nbsp;</p></div><p>&nbsp;</p></div></div>'
   should  = '<div><span style="color:#9c6500;">CAUTION:</span> This email originated from outside of the organization. Do not click links or open attachments unless you recognize the sender and know the content is safe.</div><br><div><p>actual content</p><div><p>actual content 2</p></div><p>&nbsp;</p><div><p>actual quote</p></div><div><blockquote><p>actual quote</p></blockquote></div><div><p>&nbsp;</p></div><p>&nbsp;</p></div></div>'
   result  = App.Utils.signatureIdentifyByHtml(message)
   equal(result, should)
 
+  // Invalid html signature detection for exchange warning boxes #3571
+  message = '<div>CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you recognize the sender and know the content is safe.</div><br><div><p>actual content</p><div><p>actual content 2</p></div><p>&nbsp;</p><div><p>actual quote</p></div><div><blockquote><p>actual quote</p></blockquote></div><div><p>&nbsp;</p></div><p>&nbsp;</p></div></div>'
+  should  = '<div>CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you recognize the sender and know the content is safe.</div><br><div><p>actual content</p><div><p>actual content 2</p></div><p>&nbsp;</p><div><p>actual quote</p></div><div><blockquote><p>actual quote</p></blockquote></div><div><p>&nbsp;</p></div><p>&nbsp;</p></div></div>'
+  result  = App.Utils.signatureIdentifyByHtml(message)
+  equal(result, should)
+
   // Gmail via Safari on MacOS 10.12
   message = '<div dir="ltr">Reply with <b>gmail</b> via Safari on MacOS 10.12</div><br>\
     <div>\
diff --git a/spec/lib/signature_detection_spec.rb b/spec/lib/signature_detection_spec.rb
index 53b130746..bc1dacff9 100644
--- a/spec/lib/signature_detection_spec.rb
+++ b/spec/lib/signature_detection_spec.rb
@@ -107,6 +107,21 @@ RSpec.describe SignatureDetection do
         expect { described_class.find_signature(messages) }.not_to raise_error
       end
     end
+
+    context 'when message contains exchange warning (#3571)' do
+      let(:content_type) { 'text/html' }
+      let(:messages) do
+        [
+          { content: '<div><span style="color:#9c6500;">CAUTION:</span> This email originated from outside of the organization. Do not click links or open attachments unless you recognize the sender and know the content is safe.</div><br><div><p>actual content</p><div><p>actual content 2</p></div><p>&nbsp;</p><div><p>actual quote</p></div><div><blockquote><p>actual quote</p></blockquote></div><div><p>&nbsp;</p></div><p>&nbsp;</p></div></div>', content_type: 'text/html' },
+          { content: '<div><span style="color:#9c6500;">CAUTION:</span> This email originated from outside of the organization. Do not click links or open attachments unless you recognize the sender and know the content is safe.</div><br><div><p>333 content</p><div><p>4452134123 content 2</p></div><p>&nbsp;</p><div><p>123124123 quote</p></div><div><blockquote><p>123141 144234</p></blockquote></div><div><p>&nbsp;</p></div><p>&nbsp;</p></div></div>', content_type: 'text/html' },
+          { content: '<div><span style="color:#9c6500;">CAUTION:</span> This email originated from outside of the organization. Do not click links or open attachments unless you recognize the sender and know the content is safe.</div><br><div><p>333 content</p><div><p>4452134123 content 2</p></div><p>&nbsp;</p><div><p>9999 quote</p></div><div><blockquote><p>999 144234</p></blockquote></div><div><p>&nbsp;</p></div><p>&nbsp;</p></div></div>', content_type: 'text/html' },
+        ]
+      end
+
+      it 'does not detect the warning information as signature' do
+        expect(described_class.find_signature(messages)).to eq(nil)
+      end
+    end
   end
 
   describe '.find_signature_line' do