Final answer:
In business messages, the two types of register are formal and casual, each suited to different contexts and audiences.
Step-by-step explanation:
In business messages, the two types of register are formal and casual. A formal register is typically used in professional and official communications, where the language is more structured, follows conventional rules, and often uses complete sentences and specific terminology. On the other hand, a casual register is more relaxed, can include colloquialisms, and is often used in communications with colleagues or in less formal corporate environments.
It's crucial to choose the appropriate register based on the audience and context. For instance, while communicating with senior management or external stakeholders, a formal register is most suitable. Conversely, when messaging a colleague with whom you have an established rapport, a casual tone might be more effective and appropriate.