Those conducting a mail survey for the first time are sometimes surprised by lower than expected response rates. Busy schedules make surveys a low-priority item for recipients. No mystery about the purpose of the mail survey. All recipients have access to the entire survey before filling it out.
Longer surveys look very daunting when presented on paper to respondents.
This small touch does make a difference. You can't receive a response if the survey never reaches it's destination. Use a personal signature of an appropriate company representative. If the survey is not blind, as in the case of a customer satisfaction survey, the cover letter should be signed by a high-ranking company representative. Blind surveys should be signed by the president of the research company conducting the survey.