Originally Posted by Toto

Ah yes, you can send email using any email address, as long as the IP address you are assigned matches the mail servers allowed list. It is possible to use anybodies email address as a sender, as most SMTP servers do not authenticate the email address being used, only the account username and password. As an example, I could send you an email using your email address, although of course I could not access your account because I do not know your password.

Spoofing the email address is the oldest trick in the book, and the reason why so much spam gets through, as you would hardly block emails coming from your own email address would you ?