[logback-user] smtpappender buffer size

I just upgraded from 0.9.17 to 0.9.24 and now my SMTPAppender is dysfunctional. Previously it had a BufferSize option that I had set to 1 so that I could send out a single email per error. Now I get the error and 255 of it's closest debug, info, and warn friends even though the appender is only triggered by error messages. This makes for error emails that are ludicrously long and contain 99% chaff. I need to be able to configure the SMTPAppender to be able to have a buffer size of 1. How do I do this with the latest configuration model? I looked at the docs for the evaluator, and I am unclear if this is what I have to use, and even how to use it. Help! Chris