Emails are sending successfully but keep going to spam

I've recently started having an issue where emails sent from my email account are being delivered, but some of them are ending up in the recipient's spam folder. I'm using Thunderbird and the account itself appears to be working normally. I can send and receive messages without seeing any obvious errors. I've already checked the SMTP settings, but I'm wondering if this could be related to my domain's email authentication rather than Thunderbird itself. What should I check for SPF, DKIM, and DMARC, and is there a good way to determine whether the problem is with Thunderbird, the mail server, or the domain's email configuration?