Can I run multiple domains on my Zimbra server? Does this cost more?

Yes, you can run multiple domain names on your Zimbra server and this does not cost more. Zimbra is licensed on a per mailbox basis. So you can have multiple domains delivering email to the same mailbox and the mailbox can have multiple email addresses which email is sent from. For example: Can be configured to ALL deliver to Fred's mailbox Fred can then send from any of the fred@example[1 .. 5].com or bob@ or sam@ domains.