Search Engine Optimization (SEO) is crucial in email marketing because it ensures that your content reaches the right audience. Although SEO is typically associated with website content, its principles can be applied to email marketing as well. By incorporating relevant keywords into your email content and subject lines, you increase the chances of your emails appearing in search engine results, indirectly boosting their visibility. This can lead to improved open rates and click-through rates as your emails become more relevant to your audience's interests.