On 2025-06-07 17:23, AC via Exim-users wrote:
I want to block any connection that doesn't have a successful rDNS (logs
report "no host name found") but searching around results in so many
different variants of an ACL rule to do this.
What is the proper way (likely in acl_smtp_connect if I'm not mistaken)
that will simply reject any conection that comes from a bare IP with no
rDNS? Note I'm not asking that I block something where the incoming
hostname doesn't match the rDNS where the two might mismatch (such as an
MX record vs. a more general domain), I'm only looking to block anything
that has absolutely no rDNS value so I don't want to use the
"reverse_host_lookup" option.
The closest thing I found was in the mailing list from 2008:
defer
!condition = ${lookup dnsdb{defer_never,ptr=$sender_host_address}{yes}}
message = Reverse DNS lookup failed for host $sender_host_address
Is this still a correct suggestion?
I've added a rule in acl_smtp_connect to block connections from failed
rDNS but occasionally one seemingly slips through. I suspect it's going
through a different pathway but why would acl_smtp_connect not block the
below event? There's no indication in the logs about "no host name
found". Did this go through a different ACL entirely?
SMTP protocol synchronization error (input sent without waiting for
greeting): rejected connection from H=[152.32.138.230] I=[10.0.0.6]:25
input="\026\003\001\001\027\001"
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