Example:
aol.com=%%alias%%@aol.com;;relay.isp.com
This causes that all messages for somebody@aol.com will be sent directly to relay.isp.com server instead of using standard DNS lookup for aol.com
company.com=%%alias%%@company.com;1;user:pwd@relay.isp.com
This causes that all messages for existing local user in company.com domain will be sent through relay.isp.com mail server with SMTP authentification (user:pwd) will be sent routed through relay.isp.com server
company.com=%%alias%%@company.com;;username%domain.com:passwd@relay.isp.com
This causes that all messages for somebody@company.com will be sent directly through relay.isp.com server instead of using standard DNS lookup for company.com with SMTP authentication against full email address (username%domain:password@relayserver).
localdomain.com=%%current_recipient%%;;customer-server.com
This causes that all messages for any_alias@localdomain.com will be redirected to customer-server.com, the recipient will be the primary alias of the original recipient's account