Domain Alias - Hosted
Hosted CanIt allows you to setup domain-level aliases so that, for example, email@example.com and firstname.lastname@example.org will share a single quarantine, with a single set of rules and settings, without increasing your user count for billing.
Doing so requires that both domains share a single realm and map users to the same streams.
Adding the Alias Domain
Follow the instructions here, ensuring that you select "No: Use current realm".
Once you have received confirmation, you need to go to Setup->Domain Mappings.
If you have LDAP, you should select that option as the mapping method for both the primary domain and the alias.
If you do not have LDAP, you will need to select ChopDomain. This will cause all mail to go to a stream that just uses the username portion of the email address (ie. email@example.com and firstname.lastname@example.org will both be mapped to: user).
If your primary domain had been using a different mapping method before, your users will lose access to all of the mail that has come in before the change-over. The only way to resolve this is to manually define access for each user to their old stream. It is often easier to just have the admin manage these messages. If Preferences->Quarantine Settings->S-3200 is set to "Yes", they will still be able to accept and reject mail from their old notification messages, but they will not be able to follow the the Subject links.
The old streams will expire out automatically after all of the messages in their quarantines have expired (21 days from receipt).