Here’s a very basic and brief example.

When an email provider (yahoo for example) sees someone sending spam to their users, one of the things they can do is to block that senders IP address from accessing it’s servers.

If your email provider has another user, who is sending out spam, and your IP address is the same as the spammers, your emails will also get blocked.

It would be great if someone knows of a webpage/post somewhere, which explains this in a bit more detail.

Hope that makes sense.

As a resume writer, I often caution clients that their name is the best e-mail address that they can have. It looks professional and it reduces the possibility that their important e-mails can be caught in filters. Cute names and numbers in the e-mail address are another reason spam filters grab them. When you launch an e-mail campaign, I am guessing that having a clean e-mail address of your own would also help to get things to their destination.
Julie | Resume Services´s last blog ..Plan Ahead or Prepare to Fail

Most of the email marketing programs I have used are extremely poor at delivering accurate readings, when it comes to ‘open rates’. Many give false positives and others fail to spot correctly opened emails. It’s not an exact science. I suggest you check response rates to your offers and click through to dedicated landing pages on your sites. That’s something, which is far easier to read and will give you a good idea, how many people are responding to your email marketing.

Hope that helps.