[X4U] "Mailbox full" error message?

[Robert A. (Bob) Hall]

I am getting an error message: "the destination mailbox is full ". I 
have removed many folders and messages and I still am getting the 
error message and the number of  has not changed.

Can someone explain the meaning of the message and how do fully 
correct the situation. I have assumed that it meant I had exceeded 
the allowed number of stored messages. Is there a data base I must 
reset?,etc.

Bob Hall