Net::SMTPServerBusy: 450 4.7.1 <localhost.localdomain>: Helo command rejected: Host not found

Rollbar is reporting:

```Net::SMTPServerBusy: 450 4.7.1 <localhost.localdomain>: Helo command rejected: Host not found```

MB say:

```
It looks like you're connecting to localhost.localdomain which I'd normally expect to see in /etc/hosts. It's not on your machine, do you want to 

(a) add localhost.localdomain to the hosts file?
(b) reconfigure to send to localhost in your app?
```