dehydrated/docs/domains_txt.md

domains.txt

letsencrypt.sh uses the file domains.txt as configuration for which certificates should be requested.

The file should have the following format:

example.com www.example.com
example.net www.example.net wiki.example.net

This states that there should be two certificates example.com and example.net, with the other domains in the corresponding line being their alternative names.