Email Deliverability

How to handle complaints using email Feedback Loops

It’s still quite common for senders to hold onto the false expectation that when a user no longer wants to receive email they will always click the opt-out link.

From the perspective of a users flooded inbox it’s never always going to be the case especially when you consider emails that are delivered too frequently, are badly designed, broken and other variable factors that would annoy any recipient of email.

Users will naturally look to complain because they’re not receiving what they signed up for and what senders need to do is listen to this valuable feedback.

Email Feedback Loops (FBL) are a service provided by most ISPs to help senders of email find out who’s complaining about the emails they receive.

Senders can sign-up to FBL to receive a notification each time a user marks an email as ‘Junk’.

When a complaint is received, the user needs to be opted-out and through this process there will be a reduction in complaint rates and over-time it will generate an improvement in deliverability.

ISPs want to know senders are listening to complaints from users and if the user says it’s ‘Junk’ then it’s ‘Junk’.

Microsoft’s guideline is to keep complaints below 0.3% and they also state that 30% of the IP addresses sending email to their servers is below that mark.

Return Path provide a service where they will manage FBL enrolment for senders but if you know the outbound mail server IP address(es) and you can access abuse@ or postmaster@ for your sending domain then its something you can quickly and easily do yourself online using ISP registration forms.

FBL registration and white list forms

There are more Feedback Loops and white list services available but here are links to 11 of the most popular ones.

List Unsubscribe Header

So users can click the opt-out link, mark a message as ‘Junk’ and now they can click an ‘Unsubscribe’ button outside of an email in nearly all of the popular email services such as and Gmail.

This additional method for users to quickly opt-out of receiving further emails is powered by a non-visual list-unsubscribe header that solutions like Instiller include as a standard part of delivery for bulk email.

The list-unsubscribe header (defined in RFC 2369) is optional but Gmail, for example, specifies that bulk senders must include the header.

This method is separate to FBL but it does generate a response by way of notification from the email provider.

What you need to ensure is that you’re not missing out on capturing this valuable feedback because ignoring could potentially damage your sender reputation and deliverability.

In order to increase delivery rates, make sure to encourage your users to add your email address to their address book when you send them their first email.


Complaints are never good but handling FBL complaints in the correct way not only informs ISPs that you’re taking user response seriously but it will also go some way to improving sender reputation and deliverability which naturally leads to increased campaign response rates.


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