1. Login to Smartermail > Search Domain > Manage :

2. Advanced Setting > Mail Signing > Options > Select Enable DKIM Signing > Save :

3. Generate Key > save :

4. Provide the values to customer (in this example) to add into DNS record :

dkim._domainKey.ghrh.com.my TXT p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDCVqadRmhQd+fTBRLJe0B0eMEfYlgOihZ8zVj1HCX6qcckA+UTU6edscQdD9AiNzk9doudZRoCvBxUXq2y/38jfxdcwPCW56XkOfoGJHwlh99QBdWDwASdWPFbodzdGl6fxv96FuzfFaktxWOvh5mVuYx6jKal1cpSBcX1V5SGgQIDAQAB