here's an interesting problem. we have a customer who has a sub-domain called,
say, mail_domain.customer.com
"dig mx mail_domain.customer.com" gives a normal result, answers
dc_mailhost.customer.com. 1D IN MX 10 ms1.customer.com.
dc_mailhost.customer.com. 1D IN MX 20 ms2.customer.com.
ms1.customer.com. IN A 1.2.3.4
ms2.customer.com. IN A 1.2.3.6
now, at first sight the underscore would make it all illegal, however, there's
some debate about this.
I think its illegal. I believe that an MX record is of the form:
<domain> IN MX <preference> <domain>
A hostname is really a domain with an A record, and since an underscore
("_") is illegal in a hostname it must thus be illegal in a domain name...
but my colleague disagrees and quotes the RFCs below.
The loser of this debate gets to buy the beer on payday!
Paul
---------- Forwarded message ----------
rfc1123 says
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.
but an MX record is not a hostname. In fact you can put any arbitrary
characters in a DNS zonefile, I understand that only A records HAVE to confirm
to the syntax in rfc1123.
So exim shouldn't be rejecting email for mail_domain.customer.com,
because the MX records for this domain are perfectly valid.
--
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