We have changed the limit for private messages.
1) By default you are limited to 4 private messages in each of 2 boxes.
2) After 2 days and 2 posts your limit is increased to 15 in each of 2 boxes
3) After some activity your limit is increased to 50 in each of 2 boxes.
This increase is revoked upon your first warning from a moderator.
These limits might change as we try to achieve the right balance between user convenience and forum spam.