What metrics show a successful warm-up?

Multiple metrics indicate warmup progress. Monitor them consistently.

Primary indicators:

• Gmail Postmaster Tools reputation: Should show medium to high, not low or bad
• Inbox placement: Test emails should land in inbox, not spam
• Bounce rate: Should stay below 2% (ideally under 1%)
• Complaint rate: Should stay below 0.1%

Engagement signals:

Open rates: Warmup emails should show high opens (recipients are engaged contacts)

• Reply rates: Some replies indicate real engagement
• No spam reports: Zero complaints during warmup is the target

Delivery signals:

• No rate limiting errors (421 responses)
• No blocklist appearances
• Consistent delivery without deferrals

What success looks like:

• Stable or improving reputation scores over weeks
• Ability to increase volume without metric degradation
• No sudden drops in deliverability
• Positive trajectory across all measured indicators

If any metric declines, pause volume increases and investigate before continuing.