Convertkit links appear to trigger spam filter. When I send an email and the recipient replies, the reply is caught in the spam filter. Troubleshooting this, it seems that the unsubscribe link https://unsubscribe.convertkit-mail3.com/27u908poq0tohdenlzs3 is the problem. This is shown in the first screenshot. When I remove it, the email goes through, as is shown in the second screenshot.

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