How to forward messages from PowerMTA to external SMTP servers

Example powerMTA configuration:

<domain my.forward>
 use-unencrypted-plain-auth yes
 auth-username i88ca
 auth-password xxxxxxxx
 route smtp.myserver.com:587
 use-starttls yes
 require-starttls yes
 max-smtp-out 10
</domain>
 
<domain domain-I-want-to-forward>
 queue-to my.forward
</domain>