Fixes #3344 - Allow mailto links in knowledge base (KB) and email signatures

app/assets/javascripts/app/controllers/_ui_element/richtext_additions/popup_link.coffee

@@ -21,10 +21,10 @@ class App.UiElement.richtext.additions.RichTextToolPopupLink extends App.UiEleme
   ensureProtocol: (input) ->
     input = input.trim()
 
-    if !input.match(/^\S+\:\/\//) and input[0] isnt '/'
-      'http://' + input
-    else
+    if @isWithProtocol(input) || @isRelativePath(input) || @isMailto(input)
       input
+    else
+      'http://' + input
 
   apply: (callback) ->
     input = @el.find('input').val()
@@ -57,3 +57,12 @@ class App.UiElement.richtext.additions.RichTextToolPopupLink extends App.UiEleme
     switch @selection.type
       when 'existing'
         $(@selection.dom).contents().unwrap()
+
+  isWithProtocol: (input) ->
+    /^\S+\:\/\//.test(input)
+
+  isMailto: (input) ->
+    /^mailto\:\S+@\S/.test(input)
+
+  isRelativePath: (input) ->
+    input[0] is '/'

spec/system/knowledge_base/locale/answer/edit_spec.rb

@@ -20,6 +20,45 @@ RSpec.describe 'Knowledge Base Locale Answer Edit', type: :system, authenticated
     end
   end
 
+  context 'add weblink' do
+    def open_editor_and_add_link(input)
+      visit "#knowledge_base/#{knowledge_base.id}/locale/#{primary_locale.system_locale.locale}/answer/#{draft_answer.id}/edit"
+
+      sleep 3 # wait for popover killer to pass
+
+      find('a[data-action="link"]').click
+
+      within('.popover-content') do
+        find('input').fill_in with: input
+        find('[type=submit]').click
+      end
+    end
+
+    it 'allows mailto links' do
+      open_editor_and_add_link 'mailto:test@example.com'
+
+      expect(page).to have_selector('a[href="mailto:test@example.com"]')
+    end
+
+    it 'allows link with a protocol' do
+      open_editor_and_add_link 'protocol://example.org'
+
+      expect(page).to have_selector('a[href="protocol://example.org"]')
+    end
+
+    it 'allows relative link' do
+      open_editor_and_add_link '/path'
+
+      expect(page).to have_selector('a[href="/path"]')
+    end
+
+    it 'allows non-protocol URL and prepends default protocol' do
+      open_editor_and_add_link 'example.com'
+
+      expect(page).to have_selector('a[href="http://example.com"]')
+    end
+  end
+
   context 'embedded video' do
 
     it 'has adding functionality' do