You have two options. Let's
start with the easy one:
1. (for yahoomail only) Use your original phone browser to visit
mobile.yahoo.com/mail and download your
phone's version of yahoomail software. Don't worry the website will automatically
detect you phone's version (so don't use
installed browsers like OperaMini, use the
one that came with your phone).
2. (for all email providers)The second method involves activating
the follow-come email software in your
Smart phone, this one is a bit technical,
though All you need is to fix the codes that
I'll give you. But download the yahoomail
first and tell me on this post how well it is working for your, if u are satisfied with it, then...
But if not, then go to the email settings on your phone, tell me what you see and I'll give you the required codes. Don't forget to mention your email provider eg @hotmail, @gmail, etc

With the push mail facility that comes with the phone you don't need all these headache