Sending an account invitation on Red Hat 3scale API Management spams the SMTP server

Issue

• When sending an account invitation in Red Hat 3scale API Management with an address e.g. testuser@example.com and the SMTP server does not allow to send to the provided domain e.g. example.com, the 3scale API Management sidekiq service receives the following error:

  SendUserInvitationWorker#perform raised Net::SMTPFatalError with message 550 You are not allowed to send messages to recipients outside of our organization.
  

• Invitations can either be send

  • via the Admin Portal to invite a user to an account as shown in the image
    
  • or via the Developer Portal
• Red Hat 3scale API management will retry to send this user's invitation mail multiple times per second for an infinit duration.
• This behavior may trigger DDoS and spam detection mechanisms which will block the RHOCP worker node.