When I send an email from my Yahoo account on my Blackberry?

Are you sure no one can read it? Or have you only tried one or two people? Have you tried sending an email to yourself and seeing if it is readable?

I suggest you send a Yahoo email from your blackberry to yourself and then try reading it on both blackberry and the Yahoo mail reader (on the web I mean). Then send a Yahoo email to yourself from the Yahoo mail reader (on the web) and try reading it both from the Yahoo mail reader and the web.

See if there is a difference between when you use the blackberry as either the sending or receiving device. This will help you isolate whether you are having an issue with the blackberry or with Yahoo. If you send an email from Yahoo on the web and you can read it and then you send the same thing from the blackberry and you can't read it it suggests the blackberry has something to do with the problem. If it makes no difference it suggests that the problem is with Yahoo and the blackberry is just a distraction.

I know that these steps won't immediately solve your problem but the first step is to isolate it and that will help you decide where to focus your energy. If you post your findings I can see if I can think of a next step.

try the website where u bought it from