Yes, I have proper reverse DNS and SPF records. So, I'm good to go there.

Bummer. I was hoping that earlier post about using Comcast as my relay would solve it.

Exactly. I would love to know what centralized IP blacklist that those 3 providers use.

Yes, before I brought this question to Slashdot, I did my homework first. I've scoured logs, check RBLs, used wireshark, etc. It's definitely not a misconfiguration on my end or an issue with complaints resulting from spam. The traffic coming from my server is so ridiculously small, that I was shocked to begin getting messages like these from those email providers.

The only conclusion that I can draw is that these major providers all use the same dynamic, or what they interpret as dynamic anyhow, IP lists and block based on them. I can understand that... the part that I have an issue with is that I have no recourse to have my IP reevaluated.

I have verified. I am not on any RBLs as I mentioned in my original question. As for whether or not my IP range is residential, I was told when I signed up that it was not. However, I have no way that I know of to verify that.

Yep, I've used that site and checked it against that list. 0 results found on the blacklist check.

Wow, I did not know this. This could solve all my issues. Thanks for the information, I'll look this up right away.

Yes, it requires authentication. It is definitely not an open relay or being used for spam, even by a legitimate user who may have had their password hacked or something.

Regarding the person from yahoo rejecting my email - I can confirm that's not the case. I set up a yahoo account for my self, brand new, and can't email it.

Regarding the hotmail one - I checked the logs. The average is about 3 emails a week to hotmail.

So, in other words, both of these messages are crap and not accurate.

Thanks for the reply, I appreciate it. To answer your questions:

1) Yes, I have a domain. The reverse DNS is correct and I have SPF records for the domain. Also, I'm not running an open relay and my mail server and IP address are not on any RBLs.

2) Each mail service I listed above provides different results. First, Google doesn't send me an email back notifying of an issue. They simply dump the email into the spam folder of whomever I email. Yahoo spits out several messages:

Deferred: 421 4.7.1 [TS03] All messages from XXX.XXX.XXX.XXX will be permanently deferred; Retrying will NOT succeed. See http://postmaster.yahoo.com/42...

Deferred: 421 4.7.0 [TS01] Messages from XXX.XXX.XXX.XXX temporarily deferred due to user complaints - 4.16.55.1; see http://postmaster.yahoo.com/42...

Hotmail spits back this message:

Deferred: 421 RP-001 (BAY004-MC5F24) Unfortunately, some messages from XXX.XXX.XXX.XXX weren't sent. Please try again. We have limits for how many messages can be sent per hour and per day. You can also refer to http://mail.live.com/mail/trou....

And say what exactly? They are not the problem. It's the other email providers blocking me simply because I'm on a Comcast IP.

Great. So when is the next jailbreak for 6.1.4 coming out?

RedHat should see a nice increase in business because of this.

You are absolutely correct. It is worse than locking. The Sprint and Verizon iPhone 4 and 4s are identical hardware-wise. But both companies colluded together to keep you from registering phones they didn't sell.