1) ensure you use mail.yourdomain.com (replace yourdomain.com with your actual domain) as the server, port 993, SSL/TLS for security type, and normal password for authentication.
2) in cloudflare, make sure your MX records point to the correct mail server, have a record for your mail address pointing to the correct IP address of your mail server, and set the proxy status for your mail-related DNS records to "DNS only" in Cloudflare, as Cloudflare does not proxy email traffic by default.