Change the mail relay address

If a client says to change the mail relay address When you check for new messages on your account, you are added to a list of valid senders for a period of time. Therefore, if you do not check for new messages before attempting to send or if the IP expires, then it will report this error. If your e-mail client supports it, try checking the authentication mechanism 'Log in to POP server before sending messages.' Otherwise, you can simply check for new messages and then send to correct this issue. Also note that some virus scanners, like Norton Anti Virus may cause problems with SMTP access.