Spammers can buy cheap VPS and setup all this stuff with scripts. So I don't think that it really helps. It's good to have it (to prevent spoofing), but I'm not even sure that Gmail will use wrong SPF record to deny e-mail, it's not really part of SMTP, those are just optional additions.
But volume is a good argument. I don't think that spamming could be cost-effective with something like 100 e-mails per day from a single IP-address. So why not just let small servers pass every filter in the world (may be except reverse-dns record) as long as they are small? The danger should not be very big.
Of course I might be missing something, I have no idea how spammers really operate. Or may be Google just don't care about personal servers at all.
But volume is a good argument. I don't think that spamming could be cost-effective with something like 100 e-mails per day from a single IP-address. So why not just let small servers pass every filter in the world (may be except reverse-dns record) as long as they are small? The danger should not be very big.
Of course I might be missing something, I have no idea how spammers really operate. Or may be Google just don't care about personal servers at all.