The Spanish workplace can be relaxed in person, but written Spanish tends to stay formal. A business email follows the same skeleton:

Part	Spanish	Example
Subject	Asunto	Asunto: Propuesta de presupuesto
Greeting	Saludo	Estimada Sra. García:
Opening	Apertura	Le escribo en relación con…
Body	Cuerpo	what you actually need to say
Sign-off	Despedida	Un cordial saludo, / Atentamente,

• Estimado / Estimada agrees with the person: Estimado Sr. Ruiz, Estimada Sra. García, and Estimados señores for a company. Between colleagues who use tú, Hola, Nuria: is fine.
• In Spanish the greeting ends with a colon, not a comma — Estimada Sra. García: — and the next line starts with a capital.
• Un cordial saludo is the everyday professional sign-off; Atentamente is more formal.