Singaporean culture is a mix of east and west. Singapore is less formal than many other Asian countries, but to do business in Singapore still requires proper business etiquette and extreme politeness. The first place that you are likely to encounter this is through e-mail exchanges with Singaporean counterparts.
Your standard conversational tone with new business contacts in Singapore should be formal. You may gradually become more casual over time.
Formal greetings such as "Mr." followed by a surname are appropriate. Singaporeans will quickly indicate their preferred greeting if they desire to be called something else.
Content should be amicable if other people have been copied. Confrontational content would cause both the recipient and the sender to lose face to those on copy.
"Regards" is a frequently used polite closing on business e-mail in Singapore. "Sincerely" and "yours truly" are also acceptable to use.
Hierarchy is important in Singaporean businesses. Using deference when directing an e-mail to a large group of people is always a good strategy.