Peter N. M. Hansteen asks the question, "Does Your Email Provider Know What A "Joejob" Is?" in his blog and provides some data and discussion. He provides anecdotal evidence which seems to indicate that Google and possibly other mail service providers are either quite ignorant of history when it comes to email and spam, or are applying unsavory tactics to capture market dominance.
[Ed Note: I had to look up "joe job" to find out what it is. According to wikipedia:
A joe job is a spamming technique that sends out unsolicited e-mails using spoofed sender data. Early joe jobs aimed at tarnishing the reputation of the apparent sender or inducing the recipients to take action against them (see also e-mail spoofing), but they are now typically used by commercial spammers to conceal the true origin of their messages.
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(Score: 1, Interesting) by Anonymous Coward on Monday April 25 2016, @05:23AM
How would that work?
Go online, ask the server for all your mail...
Then it asks the servers up stream for all your mail, the spammer's server would contain one message that is destined for everyone, and the intermediary servers get clogged up with spam, just as they are today.
The only way pull would fix spam is if it was also whitelist only, and whitelists are already an effective solution to spam, except you can't receive mail from unsolicited parties -- meaning that when you go register for an account somewhere, you first need to go and whitelist them in your email system before you sign up to receive the verification email. With push instead, at least you can add your whitelist entry later, and then recover the verification mail from your spam box.