There are two, major kinds of screenwriting query
letters. First, there is the traditional, paper query letter, and
second, because of today's technology, there is the email query.
Both should be presented professionally and the salutation should be a
person's name, not a company.
For example, if you are contacting an agent, it helps if
you take the time to mention a movie that this person represented and show
that you are a great fan, and if possible, know something about this
person like where they are from. Or better yet, if you know a
cousin, a colleague, a friend, mention these people, because it will be a
direct, personal connection to you.
The traditional, paper letter should be just that, in
proper format. The email query is a bit different and there are many
ways to handle this type of query letter.