Pro accounts offer access to unlimited Google Mail, Calendar & Drive accounts in one sleek, user-friendly interface. Pro also supports unlimited Microsoft Outlook.com and Office 365 accounts (including Microsoft Calendar and OneDrive accounts). For $29.99/year Pro Users can enjoy:
Support for Unlimited Accounts (Gmail, Google Inbox, Office 365, and Outlook)
Navigation Between all Mail, Calendar & Drive Accounts
Cross-Platform Support (Windows, Mac & Linux)
Access to Google Services (Contacts, Hangouts, Keep, Docs, Sheets, Slides, Photos, AdSense and Analytics)
Native Desktop Notifications
Notification Muting
Removal of the 'Sent with Shift' Signature