If you're receiving bounced (returned) emails for messages that you never sent, then this could be a case of spoofing.
Spoofing is when a spammer sends out emails using your email address in the 'From:' field. Thus your mail account gets flooded with bounce messages from the invalid email addresses in the "To:' field.
The idea is to make it seem like the message is from you – in order to trick people into opening it. The message actually originates from the spammer's email account and is sent from the spammer's email server.
We can prevent spoofing by adding a DNS record to the domain, called an SPF record. SPF is a technical method to prevent sender-address forgery by identifying which mail servers are permitted to send email on behalf of your domain.
