Senders: to join the A-List, register your domains (or email addresses) that sign with DKIM.
Receivers: if you use the Sendmail and DKIM, download the A-List milter.
The A-List will be periodically updated so additional domains and addresses can be protected. Unsigned mail can be confidently blocked.
Relevant Links
Mailbox Providers
Sender Registration
A-List Support
A-List Installation
Register your domain with the Message Level A-List
Download the Message Level A-List Sendmail Milter
Subscribe to the Message Level newsletter.
