I have set up a dynamic newsletter and the emails come from the subscriber list. The following content is present in a master page which is only used for newsletter pages.
linkSendToFriend.HRef = string.Format("ABSURL/ForwardToAFriend.aspx?r={0}", CMS.Helpers.RequestContext.CurrentURL);
The ForwardToAFriend page has 5 fields where the end user can enter 5 email addresses to send an email to them. The end user need not have to enter his own email address because he would have clicked a link in the email to come to the above page.
I am thinking if the above link can be ForwardToAFriend.aspx?r=/resources/newsletter/issue1.aspx&e=test@email.com then it will be a better user experience.