[unisog] HELO and hostname

Paul Russell prussell at nd.edu
Wed Jan 31 16:48:57 GMT 2007

On Tue, 30 Jan 2007, Bill Martin <BMARTIN at LUC.EDU> wrote:
 >Some time back, we had saw an influx of mail originating at hosts
 >providing a "helo" (hostname), where (hostname) usually started with
 >some numerical value.
 >Either I've lost my mind or there use to be an RFC that qualified
 >"acceptable" host names and if I recall, this ties in with DNS, in that
 >a hostname (especially in this case) should never start with a number,
 >only a letter.
 >Is this still an acceptable method to reject?  That is, if a host
 >announces itself as ([0-9]{x}hostname)??
 >Any help would be greatly appreciated

from RFC 1123 Requirements for Internet Hosts -- Application and Support

> 2.1  Host Names and Numbers
>      The syntax of a legal Internet host name was specified in RFC-952
>      [DNS:4].  One aspect of host name syntax is hereby changed: the
>      restriction on the first character is relaxed to allow either a
>      letter or a digit.  Host software MUST support this more liberal
>      syntax.

This would seem to indicate that rejection based solely on the fact that
the hostname starts with a digit (0-9) is probably not valid.

Paul Russell, Senior Systems Administrator
OIT Messaging Services Team
University of Notre Dame
prussell at nd.edu

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