Most ISPs block port 25 so you cannot send email from your own computer's SMTP server. This is to block spammers. If you don't intend to spam, you can use your ISP's mail server.
To get the email function from your ISP SMTP server even if you are hosting your own Joomla site on your own computer to work sign in as administrator to your Joomla site. In the menu bar: Site - Global Configuration - mail tab. Your data should look like the following:
Mailer: SMTP Server MailFrom: firstname.lastname@example.org From Name: SomeName Sendmail Path /usr/sbin/sendmail SMTP Auth: Yes SMTP User: johndoe (username at one of your email accounts at your ISP) SMTP Pass: trr33459 (password at one of your email accounts at your ISP) SMTP Host: smtp.charter.net (Whatever your ISP tells you to use for their SMTP servers)
The SMTP User, Pass, and Host are the same fields you enter when adding an Outlook Express Account, or Eudora, or any client email you may use on your computer.