Bash i/o redirection output to argument?

Say I have a one liner like

command foo | mail -s "`date +%m/%d/%Y`" [email protected]

This emails me the output of command foo as the body of an email, with the date as the subject.

But I really want the output to be in the subject line after the date, not in the body.

I know there must be a simple way to accomplish this.

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