i am assuming that you can access your email account from your main computer/laptop and are using an email program (mail.app outlook express, outlook, etc)

i would go into that mail app and look at each option and then make sure the n810's is the same....

you didnt mention if this was a webmail account (yahoo/gmail/hotmail) or from your isp or from your work... there are detailed guides on how to set up gmail here on the forum if you do a search you should be able to find them fairly easily...

if it is from your work email do they use an exchange server? is it set up for pop/imap access or only web access?