Deutsche Post to launch online secure mail service

* Still unsure how to price new offering

* Letter mail business to have stable EBIT by 2015

* Deutsche Post has no acquisition plans in short term-CEO

(Adds details, background)

HAMBURG, Nov 23 (Reuters) - Deutsche Post DHL (DPWGn.DE) is launching an online mail service in the first half of 2010 in a move to halt sliding earnings at its legacy mail business.

Customers will be able to securely send confidential business mail and official documents electronically. The company, whose letters business has traditionally been a cash cow but has been hit by e-mail and other electronic communication, will spend a double-digit million euro sum to promote the new service.

Deutsche Post, Europe's biggest mail and express delivery company, has been racing to compete with rivals like Deutsche Telekom (DTEGn.DE) which launched its own system last month.

The company has not yet decided how much to charge for the service. One option is a set fee for unlimited use over a month or a year.