He spends a lot of time dealing with business-related emails.

business-related 是由名词 business（商业、业务）和形容词 related（相关的）组成的复合形容词，中间用连字符连接。business 指"商业活动、工作事务"，related 表示"有关的、相关联的"。business-related 合起来表示"与工作/业务相关的"。