A heuristic is a bit more complex than an indexOf. I just tried it myself: An email just containing the phrase "barely legal teens" is attributed by Apples iClo

A heuristic is a bit more complex than an indexOf. I just tried it myself: An email just containing the phrase "barely legal teens" is attributed by Apples iCloud IMAP servers in the header a "spamscore" of 3 and is delivered, but marked as likely spam: > X-Proofpoint-Spam-Details: rule=notspam policy=default score=3 spamscore=3 ipscore=0 suspectscore=2 phishscore=0 bulkscore=1 adultscore=73 classifier=spam adjust=0 reason=mlx scancount=1 engine=6.0.2-1212290000 definitions=main-1302280125 I would argue that this kind of filtering is fine. Maybe it was a glitch in the server, maybe other metrics of the mail pushed the spamscore up. If iClouds Mail servers should silently decline mails for delivery is a whole different argument.