No SPF record for postgresql.org?

I've been tinkering with setting up SPF-based filtering on my mail
server, and I was surprised to find out that most of the traffic
it would want to throw away is Postgres mailing list messages.
Why is it that there's no SPF record for postgresql.org?  I realize
that there's debate about how useful SPF actually is, but surely
that's not a reason not to publish an SPF entry.
        regards, tom lane