My deliverability dropped suddenly, how do I find the cause?

Systematic cause identification:

Immediate checks:

Authentication: Are SPF, DKIM, DMARC passing? Any DNS changes?

Blocklists: Check MXToolbox, Spamhaus for IP and domain.

Postmaster: Gmail reputation, SNDS status.

Data analysis:

Bounces: New error codes or patterns?

Complaints: Spike in feedback loop reports?

Volume: Recent increases or unusual patterns?

Scope identification:

All providers or specific ones?

All campaigns or specific types?

All segments or specific audiences?

Timeline correlation:

What changed in the 48-72 hours before the drop?

List changes, content changes, infrastructure changes?

Document findings as you investigate.

Methodical investigation: was it the ship, the cargo, or the destination that changed?