"And," "But," and "Because" as Sentence Starters
Many people learned in school never to begin a sentence with and, but, or because. Presumably some teachers believe this prohibition to be legitimate, but others may have viewed the prohibition as a practical means to a pedagogical end, without necessarily believing it to be an absolute requirement for good grammar.
For example, it is easier to tell a child never to begin a sentence with because than it is to tell a child that it is acceptable to begin a sentence with because if it is the start of a dependent clause that is then followed by an independent clause, but is unacceptable if the sentence consists of a single dependent clause. (Phew!)
Clearly this is not a complete sentence:
Because I was late.
But this is:
Because I was late, I missed Jean’s presentation.
As long as you have a complete sentence, because is a grammatically legitimate way to begin a sentence — in all types of business writing. (Avoiding this structure at all costs, in fact, can create writing problems.)
In addition, you may begin sentences with and or but as long as you practice moderation and exercise good stylistic judgment. For example, a few lines up you will find a very short paragraph beginning with the word but, for a punchy, dramatic effect. And now this sentence is beginning with an and, also for dramatic effect.
Generally the more creative types of business documents, such as marketing materials, provide more opportunities to experiment with and and but at sentence beginnings than do formal documents. Even in very formal business writing, however, and and but are not banned as sentence starters. Nonetheless, you should proceed with caution.