Spoofed email domain

As the head of systems for a small business, i receive all email that is addressed to my email domain (@jlem.com) but for which there is no valid email prefix. Today, I am receiving several ‘Undliverable’ email messages that say they were sent from some random email name, but with my mail domain (@jlem.com).

I am assuming this means that my email domain was spoofed for purposes of sending a spam email.I am very concerned about the having our email domain added to black list servers and also about the the general reputation of the firm.

What can I do about this?