How do you diagnose reputation loss (Gmail Postmaster, SNDS)?

Diagnosing reputation problems requires checking multiple data sources.

Gmail Postmaster Tools:

Domain reputation: High, Medium, Low, Bad

IP reputation: Same scale for sending IPs

Spam rate: Percentage reported as spam

Authentication: SPF, DKIM, DMARC pass rates

Requires minimum volume to show data

Microsoft SNDS (Smart Network Data Services):

IP reputation scoring

Trap hit data

Complaint rates

Filtering disposition

Requires IP registration

Blocklist checks:

Use MXToolbox or MultiRBL for comprehensive checks

Check both domain and IP blocklists

Spamhaus, Barracuda, Spamcop most impactful

Some blocklists don't report publicly

Interpretation:

Single signal may be temporary; patterns are concerning

Cross-reference across multiple sources

Compare to historical baseline

Correlate with sending activity changes

Investigation questions:

What changed before reputation dropped?

Which campaigns or lists coincide with problems?

Are issues isolated to specific mailbox providers?