The read-receipt tracking stopped working, though the read-receipts icon and the link tracker icon are enabled. Is it because I have a free Mailspring account, or do I have to enable something else in options and preferences?
By the way, the icon doesn’t turn blue but is in a slightly darker grey.
It’s a per-email toggle: Read receipts are enabled individually for each email you send. Look for the eye icon in the composer toolbar when composing — click it so it turns blue/active before sending. If it’s grey, tracking is off for that email.
Pro subscription: Read receipts require a Pro subscription (free accounts get a limited number per week). If you’ve subscribed but things still look wrong, try signing out and back in at Preferences > Mailspring ID.
HTML emails only: The feature injects a tracking pixel, so it won’t work if you’re composing in plain text mode.
Recipient filtering: Many corporate mail servers and clients strip tracking pixels, so even with everything set up correctly, the receipt may not fire depending on who you’re emailing. In Gmail, recipients may need to have “Allow images from this sender” enabled. It’s often nice to use read receipts in conjunction with link tracking because link tracking is harder to circumbent and very reliable across email apps.
If the eye icon turns blue when you click it but receipts never arrive, try emailing yourself and verify that you receive a notification when you open the email.