Blocking Messages:
Server-side privacy lists enable a user to block incoming messages from other entities based on the entity's JID, roster group, or subscription status (or globally).
User blocks based on JID:<iq from='amal@example.net/home' type='set' id='msg1'>
The user will not receive messages from the entity with the specified JID.
User blocks based on roster group:<iq from='amal@example.net/home' type='set' id='msg2'>
The user will not receive messages from any entities in the specified roster group.
Blocking Incoming Presence Notifications:
Server-side privacy lists enable a user to block incoming presence notifications from other entities based on the entity's JID, roster group, or subscription status (or globally).
User blocks based on JID:
As a result the user will not receive presence notifications from the entity with the specified JID.
User blocks globally:
As a result the user will not receive presence notifications from any other users.
Note:
You can also block IQ Stanzas , outgoing presence notifications and block all communications with any user not in your roster.
blocking all communications with any user not in the roster
block communications from anyone whose subscription state is 'none'.