Yes, you may, SHADOW. I won't write a book about it, though, I warn you.
In Japanese, formal letters are written in a langauge of its own. It's nothing like what you see in newspapers or magazines. It certainly has very little in common with the kind of Japanese you guys learn outside of Japan.
Between businesses, business and individual, government and business, and gov. and ind., you will find the most formal language used along with a format expected by every party involved. Go against these rules and you will not be taken seriously.
A formal letter starts with a short paragraph of seasonal greeting. You write about what you see in nature around you at the time of the year when the letter is being written. It can be about certain trees or flowers, the temperature, weather, annual events, etc. You are expected to express not which season out of the four but what part of a particlular season. This must, however, be done with your description of the natural phenomenon and NOT by directly stating what part of the season. In other words, you cannot just say, "We are at the beginning of (insert season)." You must say, for instance, "The sakura buds have finally started opening up." This isn't always easy for the native speaker, either; therefore, there are books and websites for these phrases. You finish this first paragraph by saying that you trust that the reader stays healthy.
Then a new paragraph (maybe two or more if necessary) starts which is the actual "content" of the letter. You need to be precise and not too lengthy.
Finally the closing message comes in.
______________________
Some important points:
Throughout a formal letter, you address the reader "Family name + 様(さま)". さん is out of the question and so are any second-person pronouns.
Don't get carried away with the seasonal greeting. No one expects you to be a poet in a business letter. Don't try to be creative.
If your textbook has taught you that です/ます are polite,
forget it. Those may help you sound on the politer side in daily conversation. But in business situations, they aren't even considered "medium polite". You wil end up sounding like a dribbling junior-high student trying to talk like an adult and failing miserably. I've mentioned this on JF a few times and I get ignored each time. But I have to repeat it once again because it's true.