Macro to fold References header in news or mail onto multiple lines?

[Adam Funk <a24061@yahoo.com>]

I'm looking for an emacs macro to fold the References header in a news
or mail message that I'm editing onto mulitple lines.  I want a
command that will reformat the following line, for example,

References: <37029@invalid> <3203A@example.com> <BB6D1@invalid> <5DFF1@example.org>

into this sequence of lines

References: <37029@invalid>
	<3203A@example.com>
	<BB6D1@invalid>
	<5DFF1@example.org>

which still constitutes one header (I've used tabs at the beginning of
the subsequent lines in my example, but spaces are OK too).

(If the macro finds the References: line near the top of the current
buffer on its own, that would be nice too.)

I'm sure someone must have already done this (and I hope so, because
my elisp skills are *very* limited), but I haven't been able to find
anything relevant by googling (probably because "fold" in the Emacs
context is often used to mean hide part of a buffer from view).  I'd
appreciate a pointer to such a macro or just some more precise
terminology for googling for it.

Thanks,
Adam