Hi @Trumf,
Your command is correct and it should be able to recreate new certificate files. However, the error is from Apache. Your Apache configuration is no longer valid because it refers to the deleted files. Here, Certbot needs to use Apache in order to obtain the new certificate, but it can’t because Apache can’t even start up due to this error.
If you haven’t modified the webmail.domain-ssl.conf file, the easiest way to fix this is to delete that file so that Apache (temporarily) no longer expects the certificate files to exist.
You should also be sure that the files in /etc/letsencrypt/archive, /etc/letsencrypt/live, and /etc/letsencrypt/renewal that correspond to the files you deleted are all removed. Otherwise, Certbot may be confused because the references in /etc/letsencrypt will be inconsistent.