In accordance with best practices and industry standards, UNC e-mail administrators have taken an aggressive stance in removing spam from the UNC e-mail system. We have absolutely nothing against your mom, colleague, or friend.
UNC-Chapel Hill reserves the right to reject mail identified as spam without providing notification to the recipient. In addition, legitimate e-mail from organizations that permit the relaying of spam may be blocked, at the discretion of UNC’s system administrators, until efforts by the other organization to prevent further abuse can be corroborated.
For additional information on reducing spam, see the How do I reduce the amount of email spam I get? document.
For additional information on UNC’s spam reduction efforts, see the Server-Side Spam Filtering at UNC-Chapel Hill document.