It's not enough not to be on blacklists, Google Mail and MS Outlook online use complex, cryptic, algos to determine whether to receive mails and whitelisting someone is very far down the filter for MS (don't know about Gmail) so receiving mail you've told Outlook you want, from non-RBLed servers on long-term domains is blocked ... but you can pay to ensure the mail gets through.

We're talking single emails, in reply, from whitelisted addresses, being blocked because they come from (paraphrasing) "a server associated with a server whose IP address was previously a spam source".

That's a shared hosting experience. Mind you we were trying to send a flood of perhaps 10 emails a month to ourselves, so you can understand why they'd ignore our whitelisting./s

Not sure they've changed that much since. I have a mail server, and while it's not blacklisted by any of the bigger ones (MS, Google and so on), my whole /24 block(!) is on the blacklist of whoever is providing spam filtering to Slackware (signed up for their mailing lists while I was still using Google as a mail provider).

Because the provider says: "If you are on a network that is known for allowing email marketing to occur, you may be out of luck as well. If you aren't doing email marketing consider a different network."[0] I haven't yet gone through and actually contacted them especially since my IP is included in their "worst" category[1]. It's also the only place I've had a problem with so far, so not worth the hassle yet.

[0] http://www.mipspace.com/contact.php [1] http://www.mipspace.com/ratings.php