This is a security feature that ensures the service the website provides only goes to those authorized. This is usually done in the form of a username and password the user creates with that one service. If this is something you do often you may end up with a large number of passwords to remember. To do this you need to download a newer version of the software from the websites of the company that made your web browser. Our On-Line Help Tutorial area has a walkthrough.
Someone using an email program sends a message to an address.
Technically speaking it goes, generally, to the Internet Service Provider of the recipient. It's an issue of settings in your email program. One setting is correct, while another is incorrect. This explains why one task will work while another will not. If you cannot send, it is possible your SMTP server setting is incorrect.