Which component of email content is most likely to encourage a response from the recipient?

The call-to-action is a crucial component of email content that actively encourages the recipient to respond. This is because a well-crafted call-to-action clearly instructs the reader on what steps to take next, whether it's replying to the email, clicking a link, or signing up for an event. It creates a sense of urgency or importance, prompting the recipient to engage with the message.

In contrast, while the subject line can capture attention and the body text can provide valuable information, they do not inherently motivate action as effectively as a direct call-to-action. The signature serves a different purpose, acting more as a professional closing than an incentive to reply. Therefore, the call-to-action's role in driving immediate response makes it the most effective component in soliciting interaction from the recipient.