Expanding email aliases

[steve%prd.co.uk@localhost (Steve Blinkhorn)]

Is there a simple way of expanding an email alias, for instance
imagine utility called dealias which takes an email alias and returns
the list of corresponding email addresses to stdoutr?  I imagine it
could be done with a clever-enough use of grep on /etc/mail/aliases
and any included files, though whether I'm clever enough with grep to
write a RE for "a line starting with an alphanumeric followed by any
number of trailing lines beginning with a space character" is to be
doubted.

Any suggestions?

-- 
Steve Blinkhorn <steve%prd.co.uk@localhost>