Thunderbird

Thunderbird is free forever and open source. Its desktop application manages multiple email accounts plus calendars, contacts and tasks on Windows, macOS and Linux without ads or data-mining. An official Android application is also available. Thunderbird itself does not require an account, although the email providers you connect do.

Thunderbird is a client, not a free email account or hosted mail service. Provider settings, authentication and server quotas still apply. Built-in Exchange Web Services support on desktop is currently limited to email; Exchange calendar and address-book support and Exchange on Android are not yet included. Thunderbird for iOS is still in development, and official help is primarily community-based rather than direct personal support.

People who manage several existing email accounts and want a local, ad-free desktop client with integrated calendars and contacts.