Raikes, is one of Microsoft’s longest serving executives, will call time on his career at the Redmond, Washington-based software giant in September 2008.

Microsoft has acted quickly to replace him by hiring Stephen Elop, the COO of network equipment maker Juniper Networks, as its new president of its Microsoft Business Division which is in charge of Office productivity tools.

Elop handed in his resignation yesterday and will start at the end of January to take over responsibilities for Microsoft’s business solutions and unified communications business. Raikes however is expected to continue at Microsoft through September to ensure a smooth transition.

As part of the transition Bob Mulgia, senior vice president of Microsoft’s server and tools business will now report directly to CEO Steve Ballmer

Raikes has had a big impact during his lengthy tenure at Microsoft, almost doubling its Office, Dynamics and Exchange server business which pulls in around $16bn annually for the company. He took over the Microsoft Business Division in 2000.

Since 1981, I’ve had an incredible journey here at Microsoft. Raikes said in a statement.