I wouldn't be at all surprised to learn this isn't _technically_ true (as Matt Cutts says), but that something like it is indeed a signal in the search algorithm which in at least some cases produces the behaviour described.
I'd be very cautious advising clients to have links to their websites sent out in large, obviously spammy email campaigns.
Matt's quite likely being 100% honest when he says the domain sending the mail doesn't get penalised in search.
I wonder if he'd be quite as quick to explain whether the domains in links inside spam received by gmail are fed back into the search algorithm (or, if gmail doesn't feed that directly, whether the search team use honeypot gmail accounts to find it out themselves...)
I suspect that if the email rep theory were anywhere close to true, Google would just keep their mouths shut about it rather than tapdance around the truth.
But it might be an unintended side-effect of their obviously complex algorithm, which they are probably investigating right now.
I'd be very cautious advising clients to have links to their websites sent out in large, obviously spammy email campaigns.
Matt's quite likely being 100% honest when he says the domain sending the mail doesn't get penalised in search.
I wonder if he'd be quite as quick to explain whether the domains in links inside spam received by gmail are fed back into the search algorithm (or, if gmail doesn't feed that directly, whether the search team use honeypot gmail accounts to find it out themselves...)