The default set settings include fields with checkboxes. Unfortunately, those fields do not include "change checked to unchecked" option. This would be useful, for example, when processing returned mail, to uncheck "Send mail" for the preferred address. This could easily be fixed by changing the single checkbox to a two checkbox system, with "Checked" and "Unchecked". A field where neither is checked, would be ignored. Yet another example of programmers who don't actually use the product they design, a feature that wouldn't have taken much to implement, and which will take many years to fix.