You have the option to block a member when they send an initial message request, or after you've already accepted their message request. The member is not notified that they have been blocked, and they cannot message you again until you removed them from your blocked contacts.
Blocking a Member
When a member attempts to message you for the first time, you have the option to immediately block the member. This prevents the member from sending any further message requests (the member cannot withdraw and resend their request). The member will not be notified that they have been blocked; instead, the member will only see that you have not accepted their request.
You can also block a member you accepted a message request from who is listed in your Contacts. To block a member in your list of Contacts, find the member in the list of Contacts who are not blocked and tap the Block icon. When you block a member from your Contacts, any conversation with that member is removed from your Message Inbox.
Unblocking a Member
To unblock a member you blocked previously, find the member in the list of Blocked contacts and tap the Accept (check-mark) icon. When you unblock a member, any conversation with that member is moved back to your Message Inbox.