Sendmail is meant to be used by other apps, not by humans directly. So, its a tad confusing to use. Id recomend using nail for the job, but if you want to interface with sendmail directly,
is the way to go.. You might also find some tutorials via google.

Theres one other way, call it the lazy way I shall.. If you run your backupper via cron, and you have sendmail in place, crond will mail you all the output of any cronjob unless it has been redirected elsewhere. So, if thats in order, just echo out wha you want mailed and crond will do it for you.