Deciding whether to build or buy software for email, calendar, and contact features involves weighing customization, cost, deployment time, and resource allocation. Building software allows for tailored solutions and complete control but requires substantial resources, longer development cycles, and ongoing maintenance. Buying software offers faster deployment, reduced maintenance, and scalability, with the trade-off of less customization and potential licensing fees. The decision hinges on organizational needs, IT strategy, budget, and the importance of maintaining control versus accelerating product velocity. Companies like Nylas provide APIs that facilitate swift integration of communication features, saving development time and focusing on user experience, security, and market reach. Ultimately, the choice should align with business priorities, whether prioritizing speed and scalability or unique, customized solutions.