Tech Tip (LISTSERV) – Issue 2 – 2008

Q: What are feedback loops and why are they important to the deliverability of my email?

Answer by John Harlan
Vice President, Computer Services, L-Soft

Feedback loops are a mechanism implemented by an Internet Service Provider (ISP) to convey back to the originating mailer any complaints the ISP has received from its users regarding a specific email message. Acting on the feedback loop information, originating mailers can protect their sender reputation with the ISP by removing the complaining user (complainant) from their recipient address data.

America Online, Inc. (AOL) has long been a leader in the provision of feedback loops, which report a complaint each time AOL subscribers respond to "You've got mail!" by clicking the "This is Spam" button – whether they mean to or not, and whether they understand the implications of doing so or not.

An AOL subscriber doesn't even have to click "This is Spam" to generate a complaint. If the subscriber exits the AOL mail program with any unread email messages in the junk mail folder (i.e., items that AOL mail automatically placed in the subscriber's junk mail folder according to the system's filters, not the subscriber's filters), then AOL automatically and silently reports those unread items as spam.

Once the email message has been reported as spam – regardless of how it happened – the report constitutes a complaint and, as such, is reported back to the originating mailer through the feedback loop.

To protect its mailing reputation, the originating mailer needs to immediately and permanently remove the complainant's email address from the LISTSERV list or other mailing recipient source data (i.e., by deleting from files to be uploaded into LISTSERV or flagging it in a source database or LDAP server).

How does a mailer entity get its own dedicated feedback loop (FBL)? Several of the larger ISPs have information on their websites for requesting creation of a feedback loop. For example, as part of its Postmaster Group website, AOL has several pages of information, beginning at:, detailing the technical requirements and process for requesting a feedback loop.

With version 15.5, LISTSERV introduced support for automatically processing AOL Feedback Loop reports. (Presently only AOL's feedback loop reports are supported, but in the future, it is anticipated that reports from additional ISPs will be supported, especially as adoption of a standardized format increases.) Once a mailer entity has created its own AOL Feedback Loop and is successfully sending reports to a dedicated list on its LISTSERV server, two simple changes to the configuration – one setting added at the server level, the other setting added at the list level – allow LISTSERV to begin automatically parsing the FBL reports and taking the necessary actions to meet AOL's stringent requirements:

  • On the very first report it receives from AOL, LISTSERV performs a QUIET DELETE (i.e., without any notification to the user) on the complainant AOL subscriber email address from all LISTSERV lists on the server.
  • LISTSERV logs a SPAM_COMPLAINT entry to the changelog of the list(s) from which the complainant AOL subscriber has been deleted. SPAM_COMPLAINT entry information can be used separately to remove or flag the address in other recipient address data sources, such as Dynamic Query Lists, DBMS and LDAP servers.
  • LISTSERV performs a SERVE user OFF DROP to prevent the complainant AOL subscriber from resubscribing to any lists on the server.

This may seem harsh, especially as many AOL subscribers to LISTSERV lists who report list postings as spam do so accidentally, either by: 1.) unintentionally clicking on the "This is Spam" button (instead of the nearby "Delete" button, for instance); or, 2.) failing to examine the messages that AOL's system filters have relegated to the subscriber's junk folder and thus leaving them there when they exit the AOL mail application.

No matter: AOL treats all spam reports – intentional, unintentional or accidental – as complaints. Once submitted, the complaints cannot be withdrawn. And the complaints directly factor into calculation of the mailer entity's sender reputation at AOL, which can eventually lead to the mailer entity being completely and permanently blocked from delivering any of its mail to any AOL subscribers at all.

This leaves the mailer entity little choice but to comply as fully and completely with AOL's "one strike and you're out" rule as possible. It is to this end that LISTSERV's support for automatically processing AOL Feedback Loop reports is designed and implemented.

L-Soft offers further details in AOL Feedback Loop Auto-Processing Documentation at:

As always, L-Soft's world-class support, training and consulting staff are available to assist you with the particulars of LISTSERV support for AOL Feedback Loop auto-processing. Please contact your L-Soft sales representative at: or L-Soft customer support at: for details.

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