diff --git a/.rubocop.yml b/.rubocop.yml
index 6b7acd972..04611fe54 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -272,8 +272,6 @@ Style/MultilineOperationIndentation:
   Enabled: false
 Style/OneLineConditional:
   Enabled: false
-Style/ClassMethods:
-  Enabled: false
 Lint/Eval:
   Enabled: false
 Style/ModuleFunction:
diff --git a/app/models/channel/email_parser.rb b/app/models/channel/email_parser.rb
index 1302b4418..0b2354a31 100644
--- a/app/models/channel/email_parser.rb
+++ b/app/models/channel/email_parser.rb
@@ -573,7 +573,7 @@ end
 # workaround to parse subjects with 2 different encodings correctly (e. g. quoted-printable see test/fixtures/mail9.box)
 module Mail
   module Encodings
-    def Encodings.value_decode(str)
+    def self.value_decode(str)
       # Optimization: If there's no encoded-words in the string, just return it
       return str unless str.index('=?')