What is a subscriber ID for complaint processing and how do I implement one?

What is a subscriber ID?

A subscriber ID is an alphanumeric identifier that corresponds to a specific subscriber in your database. When you receive an ARF message from a mailbox provider indicating a complaint has occurred, you cross-reference the ID number with your database so you can suppress that subscriber from receiving future email. It is placed in your email header as an X-header.

How do I implement a subscriber ID?

Many email service providers automatically add subscriber IDs for you and may sign you up for the complaint feedback loops, but you should check with them to be sure. If you use an in-house MTA for sending bulk email, contact your email administrator or IT department to add the X-header to your emails.

  • Use a naming convention that fits in with your current company and database standards. Don't use any part of the actual email address in your naming convention, make the identifier unique and random to reduce the risk of transferring personal identifiable information to any 3rd party.
  • The subscriber ID can be a simple combination of alphanumeric characters that represent the subscriber or customer.

For example:

In your email header:      X-subID: 123456ABCD

In your database:           123456ABCD =

  • The subscriber ID can also contain other information related to that subscriber, which may be useful for other purposes related to your email program. This format is sometimes used by companies with multiple brands, countries, and list sources.
    • Using this format can be helpful when trying to identify sources of complaints.
    • Before using this format, identify data elements that are relevant to your business and that you are interested in using for segmentation or reporting purposes.

For example:

In your email header:    X-subID: ABC.123.DEF.456

In your database:    ABC.123.DEF.456 = SubscriberEmail.ListSource.Brand.Country

ABC = SubscriberEmail =

123 = ListSource = Website

DEF = Brand = Sample Brand, Inc.

456 = Country = France



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