If we have a first name, then everything is fine. However, in cases where there is no first name, there should be at least a couple of changes.
1) Allow an overall default word/phrase to use (e.g. "Subscriber", "Member", "Value Shopper, and allow that to be overridden on creation of each new draft message. That word or phrase would be plugged in if there is no first name
2) Trim extra spaces. For example, if we use the salutation "Good morning %$firstname$%." and there is no firstname value, the result is "Good morning ." i.e. there is an extra space. One space before the token (%$firstname$%) should be dropped, when the token is empty.
3) An additional, advanced option would delete the whole line and the next blank line if the user has provided "Dear %$firstname$%," and firstname is empty. Just start with the body of the email. This could be coded with an additional token such as "%$dearfirst$%". When used alone on a line e.g. "%$dearfirst$%,", or "%$dearfirst$%:", and the value of firstname is empty, then the whole line and any blank lines following, would be deleted so the email would start with the main body and no salutation.