What is the key difference between a 'lookalike' audience and a 'custom' audience within the Microsoft Advertising platform, and how do they affect campaign reach for Live.com?

The key difference between a 'custom' audience and a 'lookalike' audience within the Microsoft Advertising platform lies in how the audience is defined. A 'custom' audience is built directly from your own first-party data, such as a list of existing Live.com customers' email addresses or phone numbers uploaded to the platform. You are directly targeting individuals you already have a relationship with. A 'lookalike' audience, on the other hand, is generated by Microsoft Advertising based on the characteristics of your custom audience. The platform analyzes the demographics, interests, and behaviors of your existing customers and identifies other users who share similar traits. In terms of campaign reach for Live.com, custom audiences allow you to precisely target known users with tailored messaging, increasing the likelihood of conversion or engagement. However, their reach is limited to the size of your customer list. Lookalike audiences, conversely, expand your reach by targeting new users who are likely to be interested in Live.com's offerings based on the profile of your existing customers. They allow you to tap into a larger pool of potential customers who haven't yet interacted with Live.com but share similar characteristics with your existing user base.