In article <[log in to unmask]>,
Paul M. Karagianis <[log in to unmask]> wrote:
>I have a subscriber who is getting errors on administrative Listserv
>mail from SMTP on our IBM _and_ from LSMTP on our Alpha.  The only
>book I have here (1) with a definition of what's valid in a FQDN says
>the underscore, as used below, is legal.
 
"legal" is a funny thing here.  This was discussed a bit in RFC 1912,
but the word I like to use instead of "legal" is "safe".  The RFC's
say you can use the DNS almost any way you want, but if you want
to be safe as far as interoperability with other things like mail
then you need to restrict your character set.  That's why it's
perfectly "legal" for people like sprint to name "hosts" with
"/" characters in them, but it wouldn't be "legal" to expect
it to interoperate well.
 
--Dave