Problems with spoof, SPF

Email spoofing is when the email header's "From:" line is modified to something other than the actual original sender. A common sign that your email address is being spoofed is getting tons of spam return messages (like Failure Notification or Mailer Daemon) for emails you never sent.

One of the features of a standard SMTP server is the ability to modify the email header to be from any address. This is a convenience built in so the address is easy to read (like "bob@example.com"). This feature is often exploited by spammers trying to mask where they are sending from.

How Do I Stop Someone From Spoofing My Domain?

Unfortunately, it will not be possible to stop someone from using your email address as the "From" address. The reason for this is that the "From" address on an email works similarly to a physically mailed letter or package. You can physically put any "From" address on a letter sent via Canada Post or the U.S. Postal Service. The post office does not even check if the return address is real. It is similar with email.