User PM/PT limits are defined in the Group Permissions through the Control Panel; CP -> Permissions -> Groups. Simply choose the "Site Permission" of the group you wish to adjust (such as "Users") and change the options according to your needs:
- "Max private topics" (how many Private Topics that a user may have in their inbox)
- "Max private topic participants" (the maximum amount of people who can be involved in the user Private Topics)
- "Max posts in a private topic" (the maximum amount of posts that can be in a single Private Topic)
