Sanchit said:
Please tell me what is an SMTP Server. I want to send mass email through administration panel.
Usually, the SMTP server will be mail.yourdomain.com or may be simply yourdomain.com. Don't you use POP3 mails with your hosting? Do you use outgoing mails? SMTP server is outgoing mail server!
But check with your server administration. There are limits on number of mails sent per hour from a domain! This limits are kept to ensure that the server doesn't get blacklisted as spam server and also to ensure that one domain doesn't take up all the processing power at the cost of other sites.
@rohan: check the mail() and ini_set() function of PHP
How to Configure PHP to Use a Remote SMTP Server for Sending Mail
SETUP YOUR PHP SMTP SETTING
PHP SMTP Server (An SMTPd server written in PHP)
SMTP E-mail sending class (needs registration, free)
SMTP Auth Email Script