The companies appointed in the final part of the review fall into four sectors: field marketing, contact centres, mailing houses and data companies.
Creative and door-to-door firms were selected earlier in the year.
Under field marketing, firms selected include Carlson Marketing Group, CPM and LoewyBe. Contact centre appointments include Prolog, Two Ten Communications, Acxiom, and SR Teleperformance, while mailing houses include Vertis, Polestar and Dataforce, and data companies include Alchemetrics, The Database Group, CACI and Experian.
The COI is still to announce a small number of specialist DRM providers.
Companies faced strict selection criteria, including financial soundness and public sector experience. "COI has increased its access to suppliers with experience in engaging citizens to influence behaviour," said Marc Michaels, COI director of direct and relationship marketing.
"Reaching diverse audiences is a key element of government marketing activity. Data groups selected will offer improved analytical, profiling and segmentation capability."
Under a separate appointment - a joint initiative between its DRM team and its media and advertising services - the COI has assigned OMD Data to help it reassess its campaign planning and analysis procedures.
OMD Data is to develop a response analysis tool to help the COI create and share detailed information across government.
The system, called COI Artemis, will look at: response rates and conversion analysis; campaign planning - to ensure targets are met, the right audiences are targeted, and that lessons are learned for future activity; and task-based budget setting to evaluate what investment is needed and to optimise media combinations.
It will also look at forecasting, specifically to ensure that demand is managed through its contact centres.
The COI is looking to restructure the system to improve its communications with certain target audiences, such as the elderly, people on low incomes, parents and businesses. The challenge will be to develop a system that can cope with the different channels COI now uses.