Improved browser test.

lib/email_helper/probe.rb

@@ -382,6 +382,7 @@ returns on fail
         'Connection refused'                                        => { host: true },
         'Mailbox doesn\'t exist'                                    => { folder: true },
         'Folder doesn\'t exist'                                     => { folder: true },
+        'Unknown Mailbox'                                           => { folder: true },
       }
     end
 

test/browser/admin_channel_email_test.rb

@@ -48,15 +48,19 @@ class AdminChannelEmailTest < TestCase
 
     watch_for(
       css: '.modal',
-      value: 'already exists',
+      value: '(already exists|unknown mailbox)',
     )
 
     click(css: '.modal .js-close')
 
-    # delete
+    # delete all channels
+    loop do
+      break if !@browser.find_elements(css: '#content .js-channelDelete')[0]
       click(css: '#content .js-channelDelete')
       sleep 2
       click(css: '.modal .js-submit')
+      sleep 2
+    end
 
     # re-create
     click(css: '#content .js-channelNew')