What are signs that migration hurt deliverability?

Monitor closely during and after migration for these warning signs of deliverability damage.

Metric warning signs:

Rising bounce rates: New IPs may face stricter filtering initially, but unusual spikes indicate problems

Complaint increases: Suppression gaps or changed sending patterns triggering complaints

Open rate drops: May indicate spam folder placement (though MPP makes this less reliable)

Click rate drops: More reliable engagement signal indicating inbox issues

Reputation indicators:

• Postmaster Tools declines: Google showing reputation drop for your domain
• SNDS warnings: Microsoft flagging IP reputation issues
• Blocklist appearances: New IPs getting listed

Delivery pattern changes:

• Deferrals increasing: Providers throttling your new infrastructure
• Specific domain problems: One major provider suddenly rejecting
• Delivery slowdown: Messages taking longer to deliver

How to respond:

• Slow down sending volume
• Shift traffic back to old ESP if needed
• Review suppression list completeness
• Check authentication configuration
• Extend warmup period
• Focus on most engaged segments

If the new ship is taking on water, return to the old harbor until repairs are complete. Don't force a failing migration.