| There are three somewhat separate factions in the authentication fight. One is the ESPs, companies that send bulk mail. They send vast amounts of mail from fixed sources, referred to slightly unfairly as spam cannons. They are unusual in that they care far more than their recipients do about getting their mail delivered, and they all work for third parties so they have always wanted to be able to claim that they’re just the postman and the responsibility for abuse rests on their clients. Their mail varies from squeaky clean to rather spammy depending on the ESP. SPF and Sender-ID works fine for them since they’re all fixed sources.
The second faction is ISPs. They’re the major mail recipients, and they send a combination of normal user mail and a lot of spam from zombies. SPF works fairly poorly since they have a lot of roaming users. Web mail systems like Yahoo and Hotmail and hosting companies also fall into this category although they tend to send no zombie mail but (particularly Hotmail) spam due to crooks mechanically signing up for lots of accounts and spamming through them.
The third faction is institutions, corporate networks and the like. They tend to send modest amounts of mail and no spam since they have corporate firewalls that keep the zombie-ware out. SPF works OK for them, except perhaps for salesmen on the road, but their aggregate volume is much less than the ESPs, and the mail all goes through a central gateway so dropping in a DKIM signer wouldn’t be a big problem. |
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