I'm using Squirrel Mail...why does this message keep popping up everytime I try to delete a large e-mail?

ERROR : Could not complete request.


Query: COPY 66 ';INBOX.Trash';


Reason Given: Over quotaI'm using Squirrel Mail...why does this message keep popping up everytime I try to delete a large e-mail?
I've never used Squirrel Mail before, but ';over quota'; means you've used up too much space somewhere. Perhaps you need to empty your deleted emails folder to make room for the big email you want to delete.