What is a feedback loop (FBL)?

An FBL is an arrangement between an email sender, such as Marketo, and an Internet Service Providers (ISPs) or email hosting service.  The FBL allows the email sender to be automatically notified when the user who receives an email marks it as spam.


When a lead who uses one of these ISPs clicks the spam button for an email, the ISP sends an automated notice to Marketo. Marketo automatically unsubscribes the lead with the unsubscribe cause, "Customer Complaint Received from ISP".  Marketo's Email Compliance Team also logs these complaints for internal compliance monitoring. 


What FBLs is Marketo enrolled in?


By default, all emails sent by Marketo are covered by an FBL with the following email providers:

  • AOL
  • Bluetie/Excite
  • Comcast
  • Cox
  • Earthlink
  • Fastmail
  • Hotmail
  • IBM SmartCloud
  • OpenSRS/Tucows
  • Mail.com
  • Mail.ru*
  • QQ.com*
  • Rackspace (formerly Mailtrust)
  • RoadRunner/Time Warner
  • Synacor
  • Terra
  • United Online/Juno/Netzero
  • Yahoo!
  • Zoho.com
  • Italia Online


Marketo audits these partnerships annually, sometimes more frequently for specific partnerships.


*The FBLs for Mail.ru and QQ.com can only be set up for customer's on dedicated IPs.  Please reach out to Support if these Russian and Chinese ISPs respectively are targets for your email program.


Notably, Gmail does not offer a non-standard, proprietary FBL process in beta.  Marketo has evaluated the beta and we continue to monitor this program but have determined not to move forward at this time.