Brief Explanation catch-all email

A catch-all mailbox or address

is a mailbox to which any email not destined for a specific mailbox will be delivered. This is better explained with an example:

If you have the following mailboxes:

• john@alienhosts.com
• mike@alienhosts.com
• @alienhosts.com (the catchall)

In the above example, any email sent to john@example.alienhosts.com will be delivered to the corresponding mailbox, as will mike@example.alienhosts.com be delivered accordingly. However, what happens if an email is sent to jim@example.alienhosts.com ? As this address has no specific mailbox assigned, normally the email would be rejected with the message "user unknown". However, because of the catch-all entry, rather than being bounced the email will be delivered to the catch-all mailbox ( @example.alienhosts.com ). Similarly, any other addresses which do not have specific mailboxes assigned will be caught by the catchall mailbox and delivered to this address.