[Mimedefang] Suggestions on rejecting relays that provide syntactically-invalid arguments to HELO/EHLO

[Michael Sims]

Quoting Joseph Brennan <brennan at columbia.edu>:

> RFC 2821 says
[snip]
> so you would be wrong to say "HELO requires fully qualified domain
> name or address literal" unless rephrased to say that your system
> requires it.  In the standard it's a SHOULD not a MUST.

Take a look at the comp.mail.sendmail thread I referenced in my original post, 
they go over this point in detail.  Here is a relevant quote from RFC 2821:

---quote---
3.6 Domains

   Only resolvable, fully-qualified, domain names (FQDNs) are permitted
   when domain names are used in SMTP.  In other words, names that can
   be resolved to MX RRs or A RRs (as discussed in section 5) are
   permitted, as are CNAME RRs whose targets can be resolved, in turn,
   to MX or A RRs.  Local nicknames or unqualified names MUST NOT be
   used.  There are two exceptions to the rule requiring FQDNs:

   -  The domain name given in the EHLO command MUST BE either a primary
      host name (a domain name that resolves to an A RR) or, if the host
      has no name, an address literal as described in section 4.1.1.1.
---/quote---

Note that the word MUST appears twice in the above quote.  That appears to 
contradict the SHOULD that appeared in the section you quoted.  So, which one 
is correct?

___________________________________________
Michael Sims
Project Analyst - Information Technology
Crye-Leike Realtors
Office: (901)758-5648  Pager: (901)769-3722
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