It is the first time the group has reviewed its roster in four years. It currently retains August.One Communications, Eulogy! Cohn & Wolfe, Lansons, Shine Communications and Porter Novelli.
The new roster, which will be in place by the autumn, will see an estimated £2m a year spent in each of the next four years.
Campaigns will feature an educational drive on Royal Mail's new pricing structure and the promotion of the Post Office's home telephone service.
The group, which spans The Royal Mail, Post Office Ltd, Parcelforce Worldwide and General Logistics Services, has operated in a competitive environment this year for the first time, following a shake-up in legislation, and it now needs to see off challenges from firms such as DHL and TNT, which are coveting its business post market.
In addition, services traditionally provided by the Post Office, such as benefits and pensions, are being withdrawn as the Government turns to more efficient models such as direct payments.
While the Royal Mail Group is launching services such as banking, many post offices are now threatened with closure. '[The future of many sub-post offices] depends on how successful we are in providing and promoting new services,' said group external relations director Paul Budd.
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