How do I improve email deliverability?

Email deliverability depends on three layers: authentication (SPF, DKIM, DMARC records configured correctly), reputation (sending from a warmed-up IP with consistent volume), and content (avoiding spam trigger words, maintaining text-to-image ratio, including unsubscribe links). Start by setting up SPF and DKIM records for your domain — this alone prevents 30-40% of delivery failures. Use a dedicated sending domain (mail.yourdomain.com) separate from your main domain. Warm up new sending IPs gradually: start with 50 emails/day and increase by 20% daily over 2-3 weeks. Monitor bounce rates (keep under 2%), spam complaints (under 0.1%), and open rates. Use tools like Mail-Tester.com to check your configuration. The single biggest mistake: buying email lists. Purchased lists have 30-50% invalid addresses, which destroys sender reputation in days.