Fastmail does not support DNSSEC. If your domain has DNSSEC enabled, it can cause issues with DNS and potentially prevent you from successfully sending or receiving mail.
Below are some common issues that could occur due to DNSSEC:
- Your domain is not active, thus preventing you from sending/receiving mail.
- Your domain is active, but you're still unable to receive mail and/or mail is bouncing.
- Some DNS records are not configuring for your domain.
- You're using Fastmail to host the website for your domain, but can't enable Let's Encrypt.
If you encounter any of these issues with your domain, but your DNS records look fine otherwise, please check to see if the domain has DNSSEC enabled. If DNSSEC is enabled, disabling it should resolve the issue.
For more on why Fastmail doesn't support DNSSEC, you can view our blog post detailing this.