spamd and google smtp ips

Hi,

I'm configuring spamd and I noticed that when I send an e-mail from
GMail, each time the e-mail is submitted by a different IP address.

Here is spamdb output after sending a test email to myself:

GREY|209.85.219.182|mail-yb1-f182.google.com|...
GREY|209.85.219.177|mail-yb1-f177.google.com|...
GREY|209.85.219.176|mail-yb1-f176.google.com|...
GREY|209.85.219.172|mail-yb1-f172.google.com|...
GREY|209.85.219.180|mail-yb1-f180.google.com|...
GREY|209.85.219.175|mail-yb1-f175.google.com|...
GREY|209.85.219.173|mail-yb1-f173.google.com|...
GREY|209.85.219.179|mail-yb1-f179.google.com|...
GREY|209.85.208.46|mail-ed1-f46.google.com|...
GREY|209.85.161.52|mail-yw1-f52.google.com|...
... snip ...

Of course they are not whitelisted, as each submission
attempt is done by a different node and I guess google has A LOT of
them. I see 2 issues with that:

1) e-mail delivery takes a lot of time (as google uses exponential
backoff and stops frequent retries after few failures)

2) whitelisted IPs are more likely being expired, as my server is
not getting a lot of gmail traffic

I suppose different big e-mail providers will
have similar issues.

I'm also running BGP server to download a whitelist,
but it does not contain google servers.

Are there any solutions get around this problem? Ideally I'd like
to just whitelist reputable mail providers as I see little chance
that any spammer will outsmart Google/Yahoo/Microsoft/etc.