diff --git a/config/environments/production.rb b/config/environments/production.rb
index 4a01229..27b439c 100644
--- a/config/environments/production.rb
+++ b/config/environments/production.rb
@@ -64,7 +64,7 @@ Rails.application.configure do
   config.action_mailer.smtp_settings = {
     address: "mail.gandi.net",
     port: "587",
-    authentication: plain,
+    authentication: "plain",
     enable_starttls_auto: true,
     user_name: Rails.application.credentials.smtp[:username],
     password: Rails.application.credentials.smtp[:password]