Abstract: A method and an apparatus for collating a plurality of groups of mail items, such as flats mail, each group being pre-sequenced according to prioritized delivery addresses, into a final sequenced set of the mail items from the groups, utilizing the prioritized delivery addresses. Each bundle of mail items is formed into a single input stream of the individual mail items. The mail items are transported along a conveyor system from the input stream to a staging tower assembly. The mail items are sorted at the staging tower assembly into a plurality of subsets of mail items re-sequenced as an intermediate step to achieving the final sequenced sets. The mail items are then collated and merged into a single output stream from the respective subsets of mail items in the final sequenced set. Portions of the output stream from the staging tower assembly are collected in batches which maintain the sequence consistent with the prioritized delivery order sequence of the mail for a given carrier route.