What is the main purpose of a subject line in a business email?

The main purpose of a subject line in a business email is to summarize the email content. A well-crafted subject line gives the recipient a clear and concise indication of what the email contains, allowing them to prioritize their reading and respond accordingly. It acts as a preview or snapshot of the message, helping the recipient quickly assess its relevance. This is particularly important in a professional context, where individuals often receive numerous emails daily and need to manage their time efficiently. An effective subject line can also increase the likelihood of the email being opened and read promptly.

The other options either do not fulfill this main function or serve different purposes in the structure of an email. For instance, while greetings and closings are essential for formality and etiquette, they do not convey the essential purpose or content of the message itself. Addressing the recipient is important for personalization but does not summarize the email's subject matter, which is the primary function of the subject line.