Google’s GMail offers a free SMTP server which can be used by anyone who has a GMail account.

If you don’t have a GMail account, you can create one at the GMail account creation page. (https://gmail.google.com)

Then all you need to do is configure your mail client to use GMail for outgoing mail server. The details you should use are:

Outgoing Mail (SMTP) Server: smtp.gmail.com
Use Authentication: Yes
Use Secure Connection: Yes (this can be TLS or SSL depending on your mail client)
Username: your GMail account
Password: your GMail password
Port: 465 or 587

extra :

Log in to your Gmail account.
Click ‘Settings’ along the top of any page, and then select the ‘Accounts’ tab.
Click ‘Add another email address’ in the ‘Send mail as:’ section.
Enter your full name in the ‘Name:’ field, and the email address you’d like to send messages from in the ‘Email address:’ field.
Click ‘Next Step >>,’ and then click ‘Send Verification’ to complete the process. Gmail will send a verification message to your other email address to confirm that you’d like to add it to your Gmail account.
Now go to your e-mail client software to setup your e-mail account.
Under e-mail address, use one of the verified e-mails you’ve added to your Gmail account.
Under outgoing mail smtp server, use smtp.gmail.com. Since it requires SMTP authorization, use your Gmail account as username (e.g. yourname@gmail.com) and your Gmail password as password. You can turn TSL on or off.