Hey ElDiablo,
Here is what the dialog box says:
Mail cannot update your mailboxes
because your home directory is full.
You must free up space in your home folder before
using Mail. Delete unneeded documents or move
documents to another volume.
And then it give me the Quit...
I get this notice sometimes in Mail and it states:
"You must free up space in your home folder before using Mail. Delete unneeded documents or move documents to another volume."
There is another line above this one in the pop up box but I closed it before I could copy it. If it pops up again...