How to enable SMTP authentication?

The SMTP server does not appear to support authentication:

```
502 5.5.2 Error: command not recognized
EHLO example.com
250-3523eb956d7a
250-PIPELINING
250-SIZE 10240000
250-VRFY
250-ETRN
250-STARTTLS
250-ENHANCEDSTATUSCODES
250-8BITMIME
250-DSN
250 SMTPUTF8
AUTH LOGIN
503 5.5.1 Error: authentication not enabled
```