Notification emails from keybase marked as spam

Two emails sent to me from keybase dropped into my spam folder. I thought you'd want to know. Here are the headers. if you want a full raw .eml, email me and I'll send it.

```
X-Spam-Checker-Version: SpamAssassin 3.3.2 (2011-06-06) on oak.strangecode.com
X-Spam-Flag: YES
X-Spam-Level: ***
X-Spam-Status: Yes, score=3.5 required=3.0 tests=AWL,BAYES_50,DKIM_SIGNED,
DKIM_VALID,DKIM_VALID_AU,HTML_IMAGE_ONLY_12,HTML_MESSAGE,RDNS_NONE,
T_REMOTE_IMAGE autolearn=no version=3.3.2
X-Spam-Report:
* 2.1 HTML_IMAGE_ONLY_12 BODY: HTML: images with 800-1200 bytes of words
* 0.0 HTML_MESSAGE BODY: HTML included in message
* 0.8 BAYES_50 BODY: Bayes spam probability is 40 to 60%
* [score: 0.4024]
* -0.1 DKIM_VALID_AU Message has a valid DKIM or DK signature from author's
* domain
* -0.1 DKIM_VALID Message has at least one valid DKIM or DK signature
* 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily
* valid
* 0.8 RDNS_NONE Delivered to internal network by a host with no rDNS
* 0.0 T_REMOTE_IMAGE Message contains an external image
* -0.1 AWL AWL: From: address is in the auto white-list
```

Begin with the supplied SpamAssassin headers and obtain the full raw .eml from the reporter if needed. Compare the notification's content and delivery signals with the listed spam rules; done means identifying a concrete cause and verifying a mitigation.

Written by the indexing model from the issue text.