Receiving email on your computer or iPhone is generally easy. Sending e-mail can sometimes be a challenge. Here on Long Island, for example, Optimum Online service from Cablevision generally requires that email sent from your computer while on their network must go through Optimum's outgoing mail servers. While this might be fine for the iMac in your home or office, it becomes a problem when you sync your iPhone with the mail accounts on your computer.
Apple has put together an excellent support page to address this issue. You can find it here. In most cases, problems with sending email from your iPhone case easily be resolved.
Of course, we are always available to help as well!