We are phasing out Zendesk. Please see Discourse instead: https://community.getmailspring.com/t/cost-of-mailspring/305
Mailspring is free for Mac, Windows, and Linux! However, if you use features like Snooze, Send Later, Send Reminders and Read Receipts often, you'll need to purchase a subscription to Mailspring Pro within the app. Mailspring Pro costs $8/mo and helps support the development of Mailspring.