Why is this important?

DMARC helps prevent email spoofing by telling receiving email servers what to do if either SPF or DKIM fail authentication and alignment checks.

If you're sending emails from samplecorp.com, you should add a DMARC record to your DNS record set. In fact, Gmail and Yahoo! have recently required DMARC records for all domains that send 5,000 or more emails per day to their servers.