If you are being told that your mail server is 'broken', chances are that it is actually mis-configured.

Not having your server configured properly is a violation of RFC 2821 Section 2.3.5. The Abiliba Networks servers actually test for this, as many spammers purposely do not configure their servers properly in order to evade detection. If a server is not configured properly, the handshake protocol will fail and the email will be rejected.

Here's an example error for a broken (mis-configured) Exchange server:

 511-HELO domain 'foo.bar.local' violates RFC 2821 Section 2.3.5.
 511 Ask your system administrator to fix your broken mail server.

Note that the domain ends with ".local" -- which is not an Internet domain name. Internet domain names MUST end in ".com", ".net", ".org" or any other legal Top Level Domain Name (TLD).

A HELO without a valid FQDN ("fully qualified domain name") is blatantly illegal. It *must* be a routable domain name, not something local. So foo.local and localhost and [192.168.1.30] are illegal values. The HELO domain is supposed to let the receiving mail server know who it's talking to and a local host name just doesn't work. (Spammers and viruses love to use totally bogus HELO domains. Thus the strict filtering.)

By the way, "HELO" is part of the email handshake conversation -- the very first part. First impressions are important, even to a mail server. ;-)

Here is the text of the RFC 2821 Section 2.3.5:

   A domain (or domain name) consists of one or more dot-separated
   components.  These components ("labels" in DNS terminology [22]) are
   restricted for SMTP purposes to consist of a sequence of letters,
   digits, and hyphens drawn from the ASCII character set [1].  Domain
   names are used as names of hosts and of other entities in the domain
   name hierarchy.  For example, a domain may refer to an alias (label
   of a CNAME RR) or the label of Mail eXchanger records to be used to
   deliver mail instead of representing a host name.  See [22] and
   section 5 of this specification.

   The domain name, as described in this document and in [22], is the
   entire, fully-qualified name (often referred to as an "FQDN").  A
   domain name that is not in FQDN form is no more than a local alias.
   Local aliases MUST NOT appear in any SMTP transaction.