echo "From: from@example.comrnDate: $(date)rnSubject: subjectrnMIME-Version: 1.0rnContent-Type: text/html; charset=utf-8rnrn$(mycommandthatprintshtml)" mail someone@example.com

to: write.to@mail.com
bcc: hidden@mail.com
From: my.name@mail.com
MIME-Version: 1.0
Content-Type: text; charset=utf-8
Subject: Some subject

Dear Person,
....