Hellnet
Hellnet is an SMTP email spoofer. It uses telnet(hence the name) to access a remote mailserver and send emails as any user you wish. The address that you are mailing TO must be one the mailserver provides. Ex. you can only email to @gmail.com addresses from a google server. Also, if the address you are spoofing is not in the recipient's contacts list, your message will be marked as SPAM because of how you are sending it.