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http://www.exim.org/bugzilla/show_bug.cgi?id=485
------- Comment #3 from anomie@??? 2007-03-16 17:13 -------
On Fri, Mar 16, 2007 at 08:30:42AM +0000, graeme@??? wrote:
>
> An FQDN may not contain underscores, as per the RFCs for domain name
> construction (I forget which).
For SMTP purposes, domain name labels are restricted by RFC 2821 section
2.3.5 to consist of ASCII letters, digits, and hyphens. Later on, the
BNF also specifies that a hyphen cannot be the first or last character
of a label.
> helo_accept_junk_hosts = some.host.name:some.ip.add.ress
Note that if you set this it really will accept anything, if you just
want to accept underscores you should probably use helo_allow_chars
instead. If you do use helo_accept_junk_hosts, you would probably want
to include a rule like this in your helo ACL:
deny condition = ${if match{$sender_helo_name} \
{\N[^\x01-\x09\x0b\x0c\x0e-\x7f]\N}}
message = 501 RFC 2821 specifies US-ASCII only in SMTP commands.
Then add more rules to check for more specific syntax you want to allow.
This rule catches a few attempts per day here, I'm not sure whether it's
spambots trying to exploit holes in someone's filter or just spambots
using the compromised machine's Chinese/Japanese/Korean/etc Windos
computer name.
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