1. A method of operating a computerized device according to an electronic mail application program to selectively classify items of a set of electronic mail messages and display classified electronic mail messages to a user, comprising: receiving a user selection of an example subset of the set of electronic mail messages; performing an analysis on the example subset to find one or more shared text-based features that are shared across all items of the example subset, and based on the analysis generating a candidate classification rule identifying the shared text-based features, the analysis including multiple steps performed in sequence for respective distinct fields of the electronic mail messages, wherein in a first pass the analysis stops at a first step at which text content is found that is shared across all items of the example subset, and wherein the analysis for a next iteration continues past the first step to a second step at which text content is found that is shared across all items of the example subset; applying the candidate classification rule to the set of electronic mail messages to identify a resultant subset of the electronic mail messages satisfying the candidate classification rule, the resultant subset being a superset of the example subset; displaying the resultant subset to the user and receiving user input indicating, based on user review of the resultant subset, whether the candidate classification rule is accepted; if the user input indicates that the candidate classification rule is accepted, then finalizing the candidate classification rule into a final classification rule, and otherwise repeating the above steps one or more times for respective adjusted example subsets of the set of electronic mail messages until a respective adjusted candidate classification rule is accepted and finalized into the final classification rule, the adjusted example subset for a given repetition being formed by the user identifying a false match and/or a false non-match with respect to the resultant subset identified in the preceding repetition; and automatically applying the final classification rule in subsequent operation of the electronic mail application program to identify electronic mail messages satisfying the final classification rule and to display the identified electronic mail messages to the user in a manner reflecting their identification as satisfying the final classification rule.