confusion creating a monitor for "mail queue length"

I want to create a monitor for mail queue length,

Not sure how to proceed from this screen? Where to enter the queue size?

http://www.screencast.com/t/LESWDMAu3S2

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Howdy -- you can enter the queue size on the bottom right, next to where it says "Maximum mail queue size".

You'd also want to specify the correct Mail Server type for your system... that's usually Postfix, unless Sendmail were manually installed.

Thank you, I did not see that text entry box.