keybase email forwarding not working ("User unknown in virtual alias table")

I tried sending an email to my keybase address (larsks@keybase.io), and received:

```
----- The following addresses had permanent fatal errors -----

(reason: 550 5.1.1 : Recipient address rejected: User unknown in virtual alias tab
+le)

----- Transcript of session follows -----
... while talking to mail1.keybase.io.:
>>> DATA
<<< 550 5.1.1 : Recipient address rejected: User unknown in virtual alias table
550 5.1.1 ... User unknown
<<< 554 5.5.1 Error: no valid recipients
```

Is something broken? Or did I grossly misread something? I thought I read the email forwarding was supposed to work now.

Thanks!

Start with the reported SMTP transcript and the expectation that Keybase email forwarding should work. Determine whether the recipient address is expected to be supported, then identify the service-side cause or document the correct behavior; the issue is done when the forwarding failure has a confirmed explanation or fix.

Written by the indexing model from the issue text.