Troubleshooting a spike in complaints from a particular mailbox provider

A large number of complaints from a particular mailbox provider begin to appear when normally only a few are received each day.

Review complaint data from available sources, including:

  • Reputation Monitor
  • Certification
  • Mailbox provider complaint feedback loops (FBLs)

To resolve the problem:

  1. Determine if the complaints are coming from a small number of subscribers (for example, one subscriber complaining about a large number of messages at one time).

If so, take appropriate actions to address the issue: 

  • Remove the complaining subscriber or subscribers from your list.  
  • Monitor complaints for the next few campaigns to ensure that complaints return to normal levels.
  1. Determine if a large number of subscribers from that mailbox provider were added to your list recently.

If so, you may need to:

  • Reverse the changes or test them on a smaller group to gauge impact before rolling them out more widely.
  • Evaluate the source of the addresses and adjust how you collect them to ensure they are of the same quality as your regular list.
  1. Confirm that you actually sent the messages causing the complaints.

Fraudulent activity may be the cause if:

  • The headers in the complaints indicate the message did not come from you. In this case, your system may have a security breach and needs to be secured.
  • The FBL is domain-based rather than IP-based. This may indicate that your domain is being spoofed.
  1. Review recent changes in your mailing program that may have caused a higher number of complaints.

Consider the following:

  • Did you increase or decrease sending frequency?
  • Was there a significant change in content?
  • Did you make changes to your brand that subscribers might not recognize?

If any of these occurred, temporarily reverse the changes and communicate with subscribers so they are aware of and expect the changes.

  1. Consider other questions:
  • Did you send to a suppression list in error?

If you did, the complaints are likely temporary and will decrease over time. Make sure that you stop sending to the suppression list immediately.

  • Is the complaint handling process working properly and are complainers added to a suppression list for that mailbox provider?

Ensure that the complaint handling process for that mailbox provider is working properly and that complainers are being added to a suppression list.

  • Is your list hygiene process working properly?

Ensure that you are actively removing unresponsive subscribers, since they can sometimes be a source of complaints.

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