To open a business letter or email in Spanish, use the following greetings (saludos):
Estimado title last name: [for a man]
Estimada title last name: [for a woman]
Estimados / Estimadas [for letters or emails directed at more than one person]
To close a business letter or email in Spanish, use:
With email it's particularly tempting to use less formal language, but in a professional context and working in your second (or third!) language, it's better to stay formal and use the above terms.