diff --git a/lib/email/sender.rb b/lib/email/sender.rb
index f238e82344c..8e6435291ac 100644
--- a/lib/email/sender.rb
+++ b/lib/email/sender.rb
@@ -8,6 +8,7 @@
 #
 require_dependency 'email/renderer'
 require 'uri'
+require 'net/stmp'
 
 SMTP_CLIENT_ERRORS = [Net::SMTPFatalError, Net::SMTPSyntaxError]