Pkg exim4 users - Apr 2012 - Configuring exim4 to improve Sender-ID score?

Apologies, I previously sent my question from the wrong email address and in
rich text.
First I need to improve my mailman-bounce score! :-)
Here goes again:

It seems that Microsoft (hotmail), Yahoo!, Gmail and Apple all have different
criteria for determining the spam-scoring of emails incoming to their servers.
I''m trying to reduce the number of bounces we get as we are running a
fundraising campaign for misfitstheatre.com which is a non-profit organisation
trying to keep in touch with its stakeholders.

I think I''ve addressed the Apple and Yahoo! cases with DKIM and SPF set
up well enough for now on our website''s exim4 MTA.
We don''t seem to get as many returned emails from Yahoo! as we used to.
	? DKIM was very easy to deal with (the exim4 Debian package was there  on my
Ubuntu 11.10 dedicated server, otherwise exim4 is as I found it).
		In /etc/exim4/exim4.conf.localmacros I have just these 4 lines:
		DKIM_DOMAIN = misfitstheatre.com
		DKIM_SELECTOR = x
		DKIM_PRIVATE_KEY = /etc/exim4/dkim.private.key
		DKIM_CANON = relaxed
		and
		my public key is in misfitstheatre.com''s DNS DKIM TXT record

	? SPF: /etc/mailname is:
		misfitstheatre.com
		and
		misfitstheatre.com''s DNS SPF TXT record shows my webserver as a valid
generator of emails formisfitstheatre.com

So far so good (according to auth-results at verifier.port25.com) .... however
....
... I don''t know how to proceed to doing what  Microsoft is looking for
in its hotmail Sender ID checks.

A receiving MTA  will not find info at misfitstheatre.com (my emails''
smtp.mailfrom) on my web server.
So I will get "unable to determine PRA" ... although I don''t
really know how they do determine a PRA.
misfitstheatre.com''s MX records point to a mail server elsewhere where
misfitstheatre.com''s MTU is collocated, and not to the web server.
I don''t have a gmail account and I haven''t a clue what Google
is looking for.

I''m sure I''m reinventing the wheel here as nearly every web
site must have the same issues with trying to get their website''s
emails delivered.
I''d be very grateful for advice on how to proceed with what might make
hotmail and gmail happier to receive our (non-profit & very friendly)
emails.

I know I can improve my DKIM solution by using each website''s keys
rather than one; however, I don''t think this is relevant right now to
the hotmail and gmail issues I have.

These issues are essentially ** "what are they looking for?" and
"how can I configure exim4 to give them what they want?". **

I can Google no clear answers on Sender ID and, although I am learning a lot
about exim4 from Phillip Hazel''s "Official Guide" I
can''t help feeling that the Debian packaging offers a few choice macros
that, if I know what they were, would be as easy as my DKIM solution to use for
Sender-ID-friendly emails.