Mass mailings just don't work as well as they used to. In an employer's market, where even lousy jobs attract dozens or even hundreds of applications, quality counts for more than quantity. Identify a handful of employers you'd really like to work for and then focus your search on them. Most mass mailings look and sound mass-produced. If a new job is due to company expansion, let them know how excited you are by the prospect of working for a growing company.
Employers hire people who understand their needs.