[snip]
> Your IP address is either exhibiting suspect behavior, is
> misconfigured, or has a poor sending reputation. As a result, this IP
> is listed in the CSS Blocklist (CSS).
>
> I tried to initiate Spamhaus' delisting process, but that attempt gets
> stuck on step 2 "Troubleshooting PTR and HELO issues". Possibly because
> the server does not even listen on TCP port 25, I guess.
The PTR RR is important for outbound mail because non-authenticated
SMTP sessions will be rejected by most mail servers these days if the
IPv4 or IPv6 address sending mail doesn't have a PTR RR (and,
increasingly, most systems are requiring that the PTR RR matches with
the hostname provided by the sender's HELO or EHLO command).
For inbound mail, most systems will attempt to deliver without
bothering to check for PTR RRs. (I don't know of any off-hand that
check destinations for PTR RRs.)
> If you have ideas about what may have caused the CSS listing, or
> suggestions about how to proceed with delisting, I'd appreciate you
> sharing your thoughts. Thanks.
The CSS targets "snowshoe spamming" which is when spammers utilize a
vast quantity of IP addresses to send small amounts of eMail from
each one. It's a tactic to avoid being identified as a "bulk sender"
which is only one factor in detecting spammers.
My guess is that a spammer utilized your server's IP address somehow
to send eMail that landed in a spamtrap (or was reported as spam).
You should review your mail server's security settings, make sure it
can't be abused as an open relay (one of the easiest ways to do this
is to require SMTP Authentication for all outbound mail), and also
investigate the possibility of malicious software running on your
systems.
--
Postmaster - [email protected]
Randolf Richardson, CNA - [email protected]
Inter-Corporate Computer & Network Services, Inc.
Vancouver, Beautiful British Columbia, Canada
https://www.inter-corporate.com/
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