What is Bulk Mail?
If you are mailing one piece of mail, you put it in an envelope, seal the envelope, put a stamp on it, take it to the US Postal office and put it in the mailbox. The steps and the concept remain the same for bulk mail though there are a lot more rules and regulations. If your database has more than 200 people your mailing qualifies for a bulk mailing and the USPS will drop the postage rate they charge you for a "stamp". The amount of postage you pay for that piece of mail depends on how the mailing is prepared and if you follow all of the USPS rules you can pay as little as 20 cents in postage for each piece (less, if you are a non-profit). The savings in postage add up quickly.
Obviously, there are other reasons to take your mailing to a professional. The quality of your mailing represents your company to the public, and that means it should be a professional product. It's easier for a professional who has the tools and the knowledge of the industry to do than it is for the small business owner.