Any eMail sent to a Forwarder is sent to another eMail address. Much like the method used by the Post Office when you move; Mail sent to your old address is Forwarded to your new address.
An excellent use of Forwarders is to send eMail to a main account eMail address. Most people only need or use 2 - 4 eMail addresses or Mailboxes. Just as a Mailbox at the Post Office requires a key to open it, an eMail Mailbox requires a User ID & PW to login. A Forwarder is also an eMail address but there is no Mailbox and thus, no User ID or PW setup is required.
This means, you can have many Forwarders all going to one main eMail address. As only the main address is a Mailbox this means you can Receive and Reply to eMail sent to many addresses, using just one login.
This is a Mailbox and requires a login ID & PW
main_address@yourDomain.com
These are Forwarders and no login is required
forwarder1@yourDomain.com forwarder3@yourDomain.com forwarder3@yourDomain.com
The 3 forwarders are being sent to your "main_address@yourDomain.com" Mailbox. When you login to your "main_address" Mailbox you will be able to Read / Reply to eMail sent to 4 different eMail addresses -- and only need to know the "1" login.
Forwarders are especially useful if you need to setup temporary eMail addresses. When a Forwarder is no longer needed you simply delete it. Deleting eMail Forwarders you no longer need will help to cut down on Spam. If you haven't already, viewing the Tutorial on eMail Catch-all Settings is highly recommended.