All kidding aside, this happens for just about any subscription one signs up for; spam filters look for certain characteristics to classify email.

For example, say a company sets up an email "blast" to everyone who requested updates to an event. In order to protect the privacy of those on the list, the BCC (blind carbon copy) line is used. Since hiding a list of recipients is a hallmark of spammers, the company domain (such as "xcompany.com") is listed as meeting the "test" and the email is forwarded to the "junk" folder, which the recipient may "allow" in the future by using the controls at his or her disposal.

There are many other ways that a domain can be classified as such; in fact, most companies that are legitimate will often notify new subscribers to their newsletters or customers that it will be necessary to add the company's domain to their address books in order that the mail does not end up in the "junk" or "spam" folder.

Keep in mind that if a company even does one thing that a server (such as your internet provider or AOL, Google, Yahoo or other mail) sees as spamming, every single item sent thereafter will be marked as spam regardless of its intent or how it was generated. It's nearly impossible to get this changed, so that is why companies have decided to join them rather than beat them and educate their customers/clients, etc. to make sure that their company is listed in their address book and the mail will get through! Just for yuks, check this out: http://www.usatoday.com/tech/news/2002/01/02/harvard-spam.htm