Password incorrect error while sending Mail

An email account uses separate processes for sending and receiving. Each of these needs to have your user ID and password set up. If you can receive but not send, the outgoing (STMP) server has not been set up correctly. Usually the easiest way to fix this is to go to Settings/Mail/Accounts, tap on the account and remove it. Then restart your phone, go back to Settings/Mail/Accounts and add the account back. Your iPhone will prompt for all of the information it needs.