Sublert is a security and reconnaissance tool which leverages certificate transparency to automatically monitor new subdomains deployed by specific organizations and issued TLS/SSL certificate.
You're right! this option is not yet implemented and would make sense to resolve domains before storing them. I'll add it to the roadmap and keep this ticket open until it's released.
I tried this to list all subdomain of 0x89.me:
python sublert.py -r -u 0x89.me
However, invalid domain exists such as blog.0x89.me . Is there a way to list valid domains only at the first scan?