Sending bulk email at scale is a deliverability challenge as much as a technical one. ISPs apply reputation scoring to every sending IP and domain. These practices keep your reputation clean at volume.
IP Warming
Fresh IPs have no sending history. IP warming is the process of gradually increasing volume over days or weeks to build reputation.
A typical warming schedule for a new IP:
- Days 1–3: 500–1,000 emails/day to your most engaged recipients
- Days 4–7: 5,000 emails/day
- Week 2: 20,000–50,000 emails/day
- Week 3: 100,000–250,000 emails/day
- Week 4+: Full volume
List Hygiene
Your list quality directly determines your deliverability. A 5% bounce rate will get an IP blacklisted within days.
- Hard bounces: Remove immediately and permanently.
- Soft bounces: Retry with exponential backoff. After 3–5 consecutive soft bounces, suppress the address.
- Spam complaints: Process FBL complaints and suppress complainants immediately.
- Inactive addresses: Sunset recipients inactive for 6–12 months.
Sending Cadence
Consistency matters to ISPs. Irregular sending patterns — months of silence followed by a large blast — are a strong spam signal. Maintain consistent daily sending and ramp up gradually for large batches.
Content and Headers
- List-Unsubscribe header: Required by Gmail and Yahoo for bulk senders. Include both mailto and one-click (RFC 8058) variants.
- Plain text alternative: Always include a text/plain part alongside HTML.
- Image-to-text ratio: Aim for at least 60% text content.
- Links: Use your own domain for tracking redirects, not URL shorteners.
Bounce and Complaint Monitoring
Keep these metrics in the safe zone:
- Hard bounce rate: Under 2%
- Spam complaint rate: Under 0.1%
- Unsubscribe rate: Under 0.5%
TurboMTA's real-time dashboard shows queue, delivery and bounce state, so you can spot problems early. Pair it with feedback-loop and complaint reporting from your mailbox providers.