JAMES-3574 LMTP should reject EHLO and HELO with 500 error code
https://datatracker.ietf.org/doc/html/rfc2033#section-4.1
```
The HELO and EHLO commands of ESMTP are not present in LMTP. A LMTP
server MUST NOT return a Postive Completion reply code to these
commands. The 500 reply code is recommended.
```
A null pointer exception was generated, and the error was handled as
a transiant error, resulting in a misleading 450 code.
Other protocols backed by the protocols API are affected as well for unknown commands
(SMTP and POP3)
7 files changed
