Relevant Products: Exclaimer Cloud - Signatures for Office 365, Exclaimer Cloud - Signatures for G Suite
DMARC is an email authentication protocol which allows the owner of a domain to specify how emails are handled based on the results of SPF and DKIM checks.
Exclaimer Cloud supports the use of DMARC.
Please ensure that your domains SPF record contains Exclaimer Cloud's include mechanism.
For more information on DKIM please see Does Exclaimer Cloud - Signatures for Office 365 support DKIM?
For more information on SPF records please see Add an include mechanism to your SPF record