If you want to carry out inbound SPF, DKIM or DMARC validation on emails being sent to you from external parties you will need to configure a DNS Authentication Definition in Mimecast. The procedure is the same as creating a DNS Authentication Definition for Outbound emails but this time you will choose Inbound instead when creating it.
You will be able to choose whether to enable checks on all protocols: SPF, DKIM and DMARC or only some. You will be able to specify how to treat emails that fail any of these protocols.
Please click on the button below which will take you to the Mimecast article that explains how to achieve the above.
For information on how to configure SPF and DKIM for outbound Mimecast emails please click on the button below.