Experimental: Abstract matcher checking whether a recipient has exceeded a maximum allowed
storage quota for messages standing in his inbox.
"Storage quota" at this level is still an abstraction whose specific interpretation
will be done by subclasses (e.g. could be specific for each user or common to all of them).
This matcher need to calculate the mailbox size everytime it is called. This can slow down things if there are many mails in
the mailbox. Some users also report big problems with the matcher if a JDBC based mailrepository is used.