diff --git a/app/services/email_importer.rb b/app/services/email_importer.rb
index 55f991c..b00e83b 100644
--- a/app/services/email_importer.rb
+++ b/app/services/email_importer.rb
@@ -42,9 +42,9 @@ class EmailImporter
       end
     elsif mail.content_type && mail.content_type.match?(/\btext\/html\b/)
       plain_text = html_to_text_class.new.convert(mail.decoded)
-      if mail.content_type.match?(/\butf-8\b/)
-        # force utf-8 charset, even if we have to remve invalid characters
-        plain_text.encode!('UTF-8', 'binary', invalid: :replace, undef: :replace, replace: '')
+
+      if mail.content_type.match?(/\butf-8\b/i) and !plain_text.valid_encoding?
+        plain_text.encode('UTF-8', 'binary', invalid: :replace, undef: :replace)
       else
         plain_text
       end