Wandering Thoughts archives

Email marketing is pretty much spam

This is one of those things that I shouldn't have to write but apparently I do: anything that is called 'email marketing' is pretty much always spam, and everyone involved in it either knows this or is actively hiding their head in the sand. Theoretical good intentions in this do not matter, because there are simply too many pressures pushing the other way. There are too many reasons for salespeople to lie about whether their leads have consented to email, too many reasons for the marketing department to be optimistic, too many reasons for management to look the other way no matter what, and so on.

(One of my theories is that it has not sunk in to any layer of sales and management that email is drastically different than physical mail, not just technically but socially. Socially, I think that email is in at least some ways much more like a phone call than like postal mail. Not that this would stop some marketing organizations, of course.)

This goes at least double if you are a company that is selling 'email marketing' services to other people. Even if you desire to be entirely legitimate, it is extraordinarily difficult to avoid being exploited by the various forms of spammers (which include optimistic and willfully blind marketing departments). I'll go so far as to say that it's basically impossible to do so; the precautions necessary to not spam are uneconomic and make you completely unattractive to even legitimate companies.

(Alleged good intentions do not matter at all, of course. No one believes them, because the spammers have long since poisoned that well.)

Mapping IP addresses to ASNs

Prompted by my old SpamByASN entry, I was recently asked how you would do IP to ASN lookups, and ideally ASN to IP lookups too. Since the full answer is complicated, I will do the simple and useful one first.

Assuming that nothing funny is going on, each IP address has exactly one ASN that ultimately announces it. The easiest way to find out this mapping for a given IP address is to use the asn and aspath reverse DNS lookup zones that routeviews.org provides; these return TXT records with the relevant information. For most people, the more useful one is asn.routeviews.org:

; sdig txt 1.100.100.128.asn.routeviews.org
"239" "128.100.0.0" "16"

This says that 128.100.100.1 is announced by AS 239, using the CIDR netblock 128.100.0.0/16. (See routeviews.org for details on what is returned for IP addresses with no routing information available.)

This doesn't tell you what AS 239 is, though, and it doesn't tell you what else AS 239 is responsible for (or at least claims to route). You can look up ASN details in various registration bodies, but the simplest resource I know of is the potaroo.net AS report lookup, which for any given ASN is 'http://asNNN.potaroo.net/' (eg, ours).

Unfortunately, as far as I know looking up all of the IP addresses that belong to an ASN is harder. While potaroo.net will tell you all of the CIDR netblocks that an ASN advertises, I don't know if it will tell you if another ASN is advertising more specific routes to portions of them (which I think happens routinely). However, for anti-spam work I believe that the potaroo data is usually going to be good enough (possibly coupled with some research about what the advertised netblocks theoretically are).

Note that there are a boatload of cautions associated with using ASNs this way, which I will summarize for now by saying that the Internet does not have a consistent global view of this stuff; what you see may depend on where you look from.