In some sites/forums, certain users just use your webs for spam and sales by sending mass emails through the other's inbox messages.
It causes noise and disturb online people a lot. To deal with this issue, this add-on was born to stop that. This add-on will add a daily limit on the number of inbox message for everybody in an usergroup.By doing this, the spammers could not cross the line and we can restrict hackers and banners in general.
To set the limit for a group, when editing the permissions, under the Personal Conversation Permissions tab there is a new permission added: Daily pm limit. Leave 0 for no limit: Set the limit setting accordingly and save the changes.
For more info please check the attached screenshots.