method
delete_all
delete_all(# :yield: message)
public
Deletes all messages on the server.
If called with a block, yields each message in turn before deleting it.
Example
n = 1
pop.delete_all do |m|
File.open("inbox/#{n}") do |f|
f.write m.pop
end
n += 1
end
This method raises a POPError if an error occurs.

