Yahoo's feedback loop is different from others in that you register DKIM keys, or DomainKeys, rather than IP addresses. Yahoo will then forward spam complaint for emails signed with the DKIM keys that have been registered to the email address that you designate.
This page discusses the topic of DKIM, and how it relates to Yahoo's feedback loop in detail. If you'd like a more broad overview of Yahoo's feedback loop, including information on how to apply, then please refer to the Yahoo Feedback Loop page.
In order to sign up for Yahoo's feedback loop, you have to sign emails with DKIM.
DKIM (DomainKeys Identified Mail) is an email validation system which allows email senders to cryptographically sign messages, and email receivers to verify those cryptographic signatures. This involves a few steps:
DKIM-Signature: v=1; a=rsa-sha1; c=relaxed/relaxed; s=mandrill; d=dnscheck.co; h=From:Subject:Message-Id:To:Date:MIME-Version:Content-Type; [email protected]; bh=LFRGgsTdj2wk/cv4Wbz7vIUEynI=; b=ZvOEktkwsWwVNqBo/Kk1EfGTW/GLUg1hejOjzSf7oCsuHNnsB1JuhM9Z3DKQGJ0hAtWPAGNWs8Ns qXKN9JFDEsMOnaz4S6ySrvwRTWdafU3RArkuZvNEBPuGCmypW9RWxYW36/OqKaTHJiiD+I1/4X1O TRPj/+78vbfhSFwm58o=
Each DKIM key is uniquely identified by the combination of its domain, and it's selector. There may be many DKIM keys for a single domain name, and many DKIM keys that use the same selector, but only one valid DKIM key can exist for each unique domain name / selector combination. This is because each domain / selector combination has its own DNS TXT record, where the public key is stored.
Technically speaking, an email can be signed using any DKIM key, even if that DKIM key's domain appears nowhere else in the message. All other things being equal, it's preferable to sign the message using a DKIM that's at the same domain as the From address.