Email ---> Goes thru MLM ---> Goes through Junk Mail Filter ---> Goes
through Rules.

If an email has gone through MLM and is processed, then unless the MLM
rule specifies further processing, it really does not go any further.
This can mean that an entire set of messages may not have Junk Mail
Filter applied to them. In such a case, if the user wants to explicitly
apply Junk Email Protection to these messages in this folder, this
contextual menu item ("Apply Junk E-Mail protection") is the only way he
can do so.

Without this contextual menu item, the user really has no control over
how Junk Email protection is applied. Sometimes after using a certain
spam setting for a while, the user may decide to change it. Consider the
scenario where the user changes the spam setting from say "Exclusive" to
"High", in case a lot of legitimate email is going to Junk Email. The
changed setting will automatically only be applicable to new incoming
messages. However, if the user has a large set of emails in his Junk
E-Mail Folder and wishes to have them re-processed, then he can move
these messages out of the Junk E-Mail folder and use the contextual menu
item to apply the new spam setting to existing messages to the folder
they have been moved to (Inbox?).

NOTE: This contextual menu item is grayed out /disabled when the spam
filter setting is set to "None".