In contrast to server-based email monitoring software designed for big corporations, Email Spy does not need email server for its operation at all. Because Email Spy is being installed to each workstation, absolutely all SMTP-based emails sent by monitored users will be copied to your secret email address.
In addition to that Email Spy black-list option allows you to set flexible rules
for outgoing emails of monitored computers
(e.g. allows/forbids emails sending to specified addresses only).
That feature is very appropriate for small and middle companies,
which don't have own dedicated email server.

Click to Enable black-list filters checkbox to enable that option.
There are two filters here. First filter works by recipient address (i.e. by field To: of captured emails) and second - by sender address (i.e. by field From: of captured emails). Both filters work together. Common mask rules (where '*' substitutes any number of any symbols and '?' substitutes any single symbol) are acceptable for both filters.
Click Add... to add email address to list.
Click Edit... to change entered email address.
Click Remove to remove chosen email address from list.
Click Allow to allow sending of captured emails TO listed recipient addresses ONLY. Sending to all other emails will be forbidden.
Click Deny to forbid sending of captured emails TO listed recipient address ONLY. Sending to all other email will be allowed.
Click Allow to allow sending of captured emails FROM listed sender address ONLY. Sending from all other emails will be forbidden.
Click Deny to forbid sending of captured emails FROM listed sender address ONLY. Sending from all other emails will be allowed.
See also How to use black-list option.