eM Client's intuitive, modern UI makes it a pleasure to use, but it may not be to everyone's liking. Fortunately, you get several dozen themes and the ability to customize nearly every aspect of the UI to make it your very own.
Pricing: Free license available for two accounts; $49.95 one-time payment for the Pro version that includes VIP support, unlimited accounts, and commercial use.
Best Windows email client with a robust business platform. Since the '90s, Microsoft Outlook has been the go-to email client for businesses large and small. It's a sophisticated platform with many advanced features, but it's still relatively easy to use. And when bundled with Microsoft Office 365—a suite of several dozen productivity apps including Word, Excel, PowerPoint, and SharePoint, among others—it makes for a powerful platform. For any business that wants to buy one email client and never look back, Outlook is that platform.
Pricing: You need to purchase or own a Microsoft Office license to use Outlook (after a free trial). Office 365 Business Standard is $12.50/user/month. Note that Business Basic does not include the desktop client.