open https://gitlab.synchro.net/main/sbbs/-/issues/1028

sbl.spamhous.org will return 127.255.255.254 to indicate an invalid query, which Synchronet interprets as a spam indication:

https://administrator.de/info/spamhaus-dnsbl-return-codes-technical-update-656572.html

Also, something seems to be awry with IPv6 lookups since I get this:
`X-DNSBL: 2610:1c1:1:606c::19:2 is listed on sbl.spamhaus.org (see http://www.spamhaus.org/) as 50.16.218.27`, but a manualy lookup shows NXDOMAIN:

```
bbsdev@bbsdev:~/sbbs/ctrl % host 2.0.0.0.9.1.0.0.0.0.0.0.0.0.0.0.c.6.0.6.1.0.0.0.1.c.1.0.0.1.6.2.sbl.spamhaus.org
Host 2.0.0.0.9.1.0.0.0.0.0.0.0.0.0.0.c.6.0.6.1.0.0.0.1.c.1.0.0.1.6.2.sbl.spamhaus.org not found: 3(NXDOMAIN)
```

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