The customer agrees to refrain from sending mass, unsolicited e-mail messages. The customer agrees to post advertisements only in areas that specifically encourage or allow advertising. The customer agrees to respect the conventions of news groups, mailing lists and networks to which the customer is posting, including those more restrictive than, but not limited to the above. There are many places on the Internet where copies of UCE are re posted by recipients and system administrators in order to help notify the Internet community about where UCE is originating. First of all, you should know the difference between spam and email that is not spam.
Most people find opt-out email to be offensive and classify it as spam.
If you are sure you did not, then it may be someone attempting to appear to be a representative of the company in question, but who actually does not have the consent of the company. The main domain-name registry, Network Solutions, is a notable example of this. It has in the past sent outright spam and has been widely criticized for this action among spam-fighters. In any case, if you are sure that you did not request the email, then you are well within your rights to report it as spam. Even innocent seeming emails like petitions can circulate for years.