Apparatus, and an associated method, for alerting a respondent that generates a reply to a received mail message of addressing of the reply message to a non-secure address. A detector detects reception of a received mail message, and a correlator determines whether any of the entries on a distribution list associated with the received mail message is of selected characteristics, i.e., non-secure. If determined to be non-secure, an annunciator generates an annunciation requiring the respondent to elect whether to include the identified address as a recipient of the reply message.