Gmail is now flagging domains that do not support sending or receiving email via encryption (SMTP via TLS). While it looks like Dreamhost supports receiving emails via SMTP via TLS, Gmail is definitely flagging emails with a prominent red unlocked padlock sent from Dreamhost's mail servers.
Now that Dreamhost has finished support of the Lets Encrypt campaign for HTTPS, it would be nice if they updated the mail servers to send emails via SMTP via TLS.
More coverage on ArsTechnica: Gmail to warn you if your friends aren’t using secure e-mail.
Edit: Updated that receiving seems to be working, but sending definitely isn't.