How to use own cert and letsencrypt certs

apnow

Hi,
We are migrating our mails from multiple ISP mail systems to a dedicated server. The company owns 4 different domains, one of them with a valid SSL certificate (main domain).

We did set the SSL cert for the admin website and for the main domain (same as the MAILCOW_Hostname) and it works, but is it possible to set letsencrypt certs for the other 3 domains?

All best,
apnow