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