Google is blocking a piece of mail from me as spam. It’s individual mail directly from me to directly one other person. It has no images or links and is plaintext. I’m asking someone I know for recommendations for a fill-in slot at a music festival.

Any ideas? The page linked in the bounce is pretty much useless, and I’m worried they’re trying to force everybody to adopt DKIM, which is a tremendously broken standard I’ve addressed before.

  ----- Transcript of session follows -----
... while talking to
<<< 550-5.7.1 [2601:8:9740:1300:da50:e6ff:fe55:2303      12] Our system has detected
<<< 550-5.7.1 that this message is likely unsolicited mail. To reduce the amount of
<<< 550-5.7.1 spam sent to Gmail, this message has been blocked. Please visit
<<< 550-5.7.1 for
<<< 550 5.7.1 more information. g5si6986243pdc.141 - gsmtp
554 5.0.0 Service unavailable
Reporting-MTA: dns;
Received-From-MTA: DNS;
Arrival-Date: Wed, 17 Dec 2014 11:46:08 -0800

I tried a shorter one, and it's bounced as spam too:

From: "Dara Korra'ti (public)" <[deleted]>
Subject: how about this one?
Date: December 17, 26 Heisei at 11:46:07 AM PST
To: (account withheld}

does it like this short one? If so, check your FB, Google is blocking email from me to you. :(

We have an SPF record, and this is a new trick we've only detected today. Some mail can get through to other people, but none to this recipient. But the original mail which triggered the first bounce can get through to no one. Thoughts?