How do you send an email back to sender?

Nope. You can reply or forward it back but you still received it.*


*Not necessarily true. Under certain circumstances, i.e. you are willing to block the sender altogether (this can always be undone later if you wish), then yes, this can be done. Some spam filters (some free, some not) offer this capability as an option, but depending on the filter, it can be confusing to configure. Perhaps the easiest way to "return to sender", then, is to use the free Windows Live email client, though you must have a POP/SMTP account (in other Words, an email account you can access with desktop email applications such as Outlook Express, Mozilla Thunderbird, etc.). If you're uncertain about this, refer to the help section of your email service or contact your ISP.

To set the feature up in the Windows Live email client, use the menu bar at the top of the screen and select as follows: Actions->Junk Email->Safety Options... then select the Blocked Senders tab. At the bottom of the screen under the phrase "When I delete and block" is a check box next to the option "Bounce the blocked message back to the sender". Check this box.

After that, any time you block a sender using the Windows Live email client (while highlighting email from the sender you'd like to block go to: Actions->Junk Email->Add sender to blocked senders list), the sender's email will be moved to the Junk email folder where you can delete it, thus bouncing the email back to the sender.

Please note, while technically correct in the assertion of the first answer ("you still receive it"), you're receiving the message into your junk folder and the process is fairly automated and substantially different from both forwarding and replying. In the end, you should get the desired effect of sending the sender the "don't even bother" message you are probably striving for.

On the Apple™ Computer Mail Application, right click, then select bounce.