Outlook 2010 strange characters on Sent Items folder

Dear All,

I've Outlook 2010 on my machine and i noticed that some of sent emails, sent with strange characters and the original characters wrote on Arabic. And when i came back to check my old emails on sent items i noticed that some of them converted to strange characters also. Knowing that they were correct on the past. I searched on internet and i didn't find the solution. Please help me because those emails are very important and i don't want to lose them.

Thanks in advance.