You can disable read receipts and / or link tracking by unchecking these icons when composing your email. Mailspring remembers your settings—after turning these features off, they’ll remain disabled for new drafts until you enable them again.

When link tracking is on, the links in your message are rewritten to go through link.getmailspring.com so clicks can be counted before the recipient is sent on to the real address. Turning link tracking off sends your links exactly as you wrote them.