Actually, I didn't lost anything, because I can see those pms from the ACP. But in my user control panel, I don't see more than 3 pages of pms (that means 75 pms, 25 every page) with a first in/first out system... Every new PM, I lose the older one.
Other users don't have this problem cause they can never reach 75 PM (limit is 50)... but I as admin can't see all my pms

What could the problem be?
Edit: I investigated further, analising my inbox and ACP at the same time.
The control panel can't show more than N° messages. When my inbox is full and I receive a new message, I loose the older one I have.
But actually I don't lose it, till it remains in the sentbox of the sender, in fact, from ACP I can see that all my pms older than the last one I "lost" are marked as "PMs sent". So I can assume that when I have inbox full, I receive a new message and my older one got deleted.
So two questions:
1. Why doesn't the admin have infinite quota for pms? (Ehm... I am supposing the high quota is 75 because with inbox full I have 75 messages, but I didn't find the quota configuration for pms in ACP... can someone help?

2. Does the normal user lose his last PM when the inbox is full and he receives a new PM?
I ask these questions because I think it could be useful for the admin to have infinite pms, and for the users to block pms receptions and receive instead and advise in order to backup their pms if they want. What do you think about it?
If there is something I am wrong with and I don't know, please correct me.