Gary Funck wrote:
But isn't it likely that if spammers are going to the trouble to add SPF records that they're also going to the trouble to retry after a tempfail, and thus defeat greylisting?
They haven't so far, and they've been using SPF records for, what, two years now? Some groups of spammers were among the early adopters, because they thought it would get them a free ride past filters.
Of course, It's much easier to add "v=spf1 +all" to your DNS than to write an smtp client that will retry every delivery attempt in a situation where you expect most of your output to get blocked, dropped, or hidden. Why waste the time and bandwidth? It may not be your own connection anymore, but hey, access to those botnets costs money!
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