What Affects Deliverability?
Email deliverability is determined by multiple factors. Even with correctly configured mail servers, your messages may land in spam if your reputation is poor.
Authentication (Required)
- SPF — defines which IPs can send email for your domain
- DKIM — cryptographically signs messages
- DMARC — tells receivers what to do with failed SPF/DKIM
- rDNS/PTR — IP maps back to your mail hostname
IP Reputation
Your server IP has a reputation score maintained by services like:
- Spamhaus
- Barracuda
- Microsoft SNDS
- Google Postmaster Tools
Check Your Reputation
# Check major blacklists
# Use MXToolbox.com or manually:
dig +short your-ip.zen.spamhaus.org
# Empty result = not listed
# 127.0.0.x = listed (check Spamhaus for reason)Warming Up a New IP
New IPs have no reputation. Start slowly:
- Week 1: Send 50-100 emails per day
- Week 2: Increase to 500 per day
- Week 3: Increase to 2,000 per day
- Gradually increase volume over 4-6 weeks
Best Practices
- Never send unsolicited email (spam)
- Include an unsubscribe link in bulk email
- Keep bounce rates below 2%
- Monitor spam complaint rates
- Remove invalid addresses promptly
- Use a dedicated IP for transactional email
Transactional vs Marketing Email
Consider separating transactional email (password resets, order confirmations) from marketing email. Use different IPs or subdomains so marketing reputation does not affect critical transactional delivery.