Os limites de SCL se aplicam, na verdade. TechNet diz:
You can customize how the Content Filter agent assigns SCL values by configuring custom words. Custom words are individual words or phrases that the Content Filter agent uses to apply appropriate filter processing. You configure approved words or phrases with Allow phrases and unapproved words or phrases with Block phrases. When the Content Filter agent detects a preconfigured Allow phrase in an inbound message, the Content Filter agent automatically assigns an SCL value of 0 to the message. Alternatively, when the Content Filter agent detects a configured Block phrase in an inbound message, the Content Filter agent assigns an SCL rating of 9.
You can enter custom words or phrases in any combination of uppercase and lowercase letters. However, when the Content Filter agent evaluates message content, it ignores case. The maximum number of custom words or phrases that can be created is 800.
Você precisa entrar e informar ao Exchange o que ele deve fazer com essas mensagens baseadas no SCL . Se você deseja que as mensagens sejam excluídas, é necessário informar ao Exchange para excluir mensagens com um SCL de 9 (pelo menos).