From RFC2821:
To promote interoperability and consistent with long-standing guidance
about conservative use of the DNS in naming and applications (e.g., see
section 2.3.1 of the base DNS document, RFC1035std13 [22]), characters
outside the set of alphas, digits, and hyphen MUST NOT appear in domain
name labels for SMTP clients or servers. In particular, the underscore
character is not permitted. SMTP servers that receive a command in which
invalid character codes have been employed, and for which there are no
other reasons for rejection, MUST reject that command with a 501
response.
On Thu, 16 Dec 2004 12:00:02 +0000
exim-users-request@??? wrote:
> From: Marc Perkel <marc@???>
> To: exim-users@???
> Subject: Re: [exim] syntactically invalid argument(s) - rejected HELO
> Date: Thu, 16 Dec 2004 03:39:19 -0800
>
>
>
> Igor Robul wrote:
>
> > Marc Perkel wrote:
> >
> >> I have a customer who is getting real email from korea (yes - there
> >> is email that isn't spam) . But - getting this in the logs.
> >>
> >> syntactically invalid argument(s)
> >>
> >> What does this mean?
> >>
> > Does host name in HELO contain underscore? We have one Vietnamese
> > client who has '_ ' in HELO.
> > Put
> > helo_allow_chars = _
> > in your exim configuration file.
> >
> Yes - I think that's it! So - why is an underscore a reason for
> rejection?
>
--
Nikademus
http://www.octools.com
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