Jeff Chan jeffc@surbl.org writes:

1. We had discussed two strategies for a combined list A records before:

We still don't really care as long as you don't it right. :-)

If you think you might end up supporting more than 32 return codes (seems like a very remote possibility), separate A records is much easier. Maybe that helps make up your mind.

So the code using a combined list could be made to detect specific results, i.e., the specific list which triggered a matching A record could be determined, and not just that it matched "all" or any from the original list. On the other hand, the fact that matches from any list occurred may be good enough for some users. Personally I prefer more a detailed explanation

A more detailed explanation is merely the job of the client. If a client can't handle multi-DNSBLs, then it's really behind the times. Given that these clients are going to need to parse URIs and that is non-trivial, I think you can just require multi-DNSBL support for newer lists at some point if you want.

2. Another question would be the name of the combined list. Since

there would be three or more lists, someone had suggested a name of "all" before. That sounds good to me unless there are other suggestions.

"query" and "bl" are two somewhat more common names for a single combined blacklist.

3. I'm assuming TXT records are no longer really feasible in a

combined list and that descriptive messages will need to be signalled by the list (127. address) matched. I suppose it would be possible to create custom TXT records for every entry, but a generic TXT (or perhaps none) might be more likely. Is a generic TXT better than none? Even in a BIND file, where it incurs some use of space?

You could return a single URL that if loaded contains information about exactly which lists hit. You can also return multiple TXT records that can be matched as SpamAssassin rules (yes!), but unless you promise to keep the format very very stable, then we'll just use the A records.

My suggestion: start with the A and worry about the rest later.

4. TTLs: If an entry has matches on more than one list, should

it get a unique TTL? If so, should such a custom TTL on the multiply-matching entry be the longest TTL or the shortest TTL? I lean towards the inheriting the shortest TTL from the matching source list, plus setting a default TTL for the combined zone file to be near the longest. [...]

Sounds fine to me.

5. We will likely want to combine the ws and be lists into a

single entry in a combined list, probably using the .1 bit for both of them, since both lists contain the enumerated (non-wildcarded) domains from SA regular expressions. Also, things are moving towards combining the non-wildcarded domains sa-blacklist and BigEvil/MidEvil, so this would somewhat short-circuit that process and future-proof things.

As long as they have similar S/O ratios, I'm okay with it. If they are maintained separately, it might shift the decision towards keeping them separate, but if they're getting merged, then that makes more sense.

Daniel