Now buffer handler never resets the buffer, and the $level argument is
what used to be flush level. When level is met or exceeded, the tail
buffer will be flushed and the underlying handler will handle them as a
batch. So if using with an email handler, you'll get an email for every
critical+ by default, and for each one of those you will get the 25
previous logs, no matter what their level was. If that is information
overload it would be suggestible to put a FilterHandler in front of
this.