Spoofing a Common Technique Used by Spammers.
Now-a-days, spoofing has become a very common technique in viruses adopted by spammers. There is no fool proof technique to avoid spammers spam the inbox with unwanted e-mails. In spoofing it is not necessary that the spammer is using your mail server to spoof your mailbox.
E-mail spoofing
The spammers sends a genuine e-mail to [...]