For the most part, the process of proofing business correspondence is the same as any other writing. There has to be a drafting process and the proofreading process might take multiple times. This is to ensure that proper grammar has been employed, correct spelling and punctuation are present, and that the mechanics of writing reflect the gravity of the correspondence. Good writers are good readers and both complement one another when proofreading.
One area that is a higher level of proofreading would be to examine content in a careful manner. The correspondence should be expressing what the business person wants it to express. It should not include anything that could be used later as a reference point to put the individual or organization in a bad or compromising light.
Reading business correspondence over to ensure that communication is clear and not binding is critical. Since all correspondence that is generated in the business setting can be used later on as a reference point, it is important to ensure that clarity and a sense of exactitude in writing is evident. Proofreading to see that correspondence is aligned with company positions or "the company line" can help to accomplish this end.