Reinstalled Windows 7 and Windows Live Mail 2011 three weeks ago at which time I imported my contacts which I had exported before the reinstallation.

Since the reinstallation I have been able to receive and send to the contacts I had before the changes but whilst I am receiving emails from new contacts I can no longer either send or reply to these new contacts. At the moment I am getting round the problem by sending and replying to new contacts by using an alternate mail service I have. How do I overcome this problem?