[unisog] DNS Hostname and SMTP Helo

Valdis.Kletnieks at vt.edu Valdis.Kletnieks at vt.edu
Tue Jan 30 20:54:03 GMT 2007


On Tue, 30 Jan 2007 13:58:13 CST, Bill Martin said:
> 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.  

Then this company called '3Com' started making these cards, and wanted a domain...

RFC1123, from way back in October 1989 says this:

   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.

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