Dear friends,
May you face after installing Forefront Protection for Exchange, Outlook’s “Block Sender” does not work and Exchange’s IMF (Internet Message Filter) functionality fails to work as well.
The cause of that is by default when Forefront’s anti-spam agent deems a piece of mail as non-spam (clean) it sets the SCL rating of that specific message to –1. This has a negative effect on the Outlook “Block Sender” functionality, and Exchange’s IMF, because mail that receives a rating of SCL -1 will be exempt from Outlook’s Block Sender rule as well as Exchange’s IMF functionality.
The workaround is to edit the SCL value that Forefront Protection for Exchange applies to “clean messages”.
The following work around will change the Forefront Protection for Exchange SCL clean value to zero (0). This is done in Forefront’s Power Shell by creating a new extended option:
PS> New-FseExtendedOption –Name CFAllowBlockedSenders –Value true
PS> Get-FseExtendedOption –Name CFAllowBlockedSenders
This should return the following: CFAllowBlockedSenders True
Now you can test your outlook after blocking someone what happen 
