[Mimedefang] Revisit: Filtering on HELO

James Ebright jebright at esisnet.com
Mon Mar 19 11:05:46 EDT 2007

On Sun, 18 Mar 2007 09:47:38 -0400, Kevin A. McGrail wrote 
> No, I don't believe it would because this is in the definition of 
> the FQDN not the IP Literal.
> Unfortunately, I don't believe the FQDN definition changes my 
> original statement.

Let me say, my HELO/EHLO filering is pretty much identicle to KAMs, and I have
had few if any complaints running it for several years now.

Here is the section of the RFC sepcific to domains that I believe resolved
most if this argument:
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

   -  The reserved mailbox name "postmaster" may be used in a RCPT
      command without domain qualification (see section and
      MUST be accepted if so used.

This pretty much spells out exactly what is required when domain naames are
used within SMTP communications. 



James R. Ebright
ESISnet    252.672.5600

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