edm customer loyalty SPAM-free email Email Marketing email gmail sender reputation subscribers tips edm design send list unsubscribe CRM bounce Segmentation personal email SMS marketing Effective subject lines eCRM signup form engagement rate Call To Action survey CTA Autoresponders preheader brand mobile drip marketing Facebook responsive marketing 社交媒體 email market 垃圾郵件 Gmaii 情感營銷，價值營銷 DNS responsive-eDM SPF Christmas DKIM promotion. eDM marketing DMARC SMS eCard eCRM，顧客關係管理 online shop direct mailing 2017 Email Marketing whatsapp Tel personalize relation content