Check a Cold Email List Against Your Global Suppression List (Free Tool)

Why Suppression Fails in Real Operations

Nobody decides to email their customers cold; it happens structurally. Unsubscribes live in the sequencer, customers live in the CRM, bounces live in a verification export, the do-not-contact spreadsheet lives with legal, and the new campaign launches from a fresh Apollo export that has never met any of them. Five sources of truth, zero enforcement between them. The fix is not more discipline, it is a gate: one mechanical check that every list passes through between export and import. Gates work because they do not rely on anyone remembering.

The Three Matches That Matter

• •Exact email match: the baseline. Case-insensitive, whitespace-trimmed, run against every suppression source at once. Catches the contact who unsubscribed last quarter appearing in this quarter's export, which happens constantly because data vendors re-sell the same records.
• •Company domain match: the one everybody skips. Extract the domain from every suppressed email, add any explicitly suppressed company domains, exclude free providers, and remove every campaign contact whose domain matches. This catches new hires at previously contacted companies, colleagues of the person who said stop, and contacts at customer accounts your CRM does not know about.
• •Account collision check: suppression's sibling. Within the campaign itself, count contacts per company domain; more than 2-3 contacts hitting one company in the same campaign reads as an attack on their mail filter and gets your domain blocked for everyone at once. Full treatment in our domain suppression guide.

The Monthly Suppression Workflow

WEEK 1 OF MONTH
1. Export customers from CRM        -> customers.csv
2. Export unsubscribes + negatives
   from every sequencer workspace   -> optouts.csv
3. Export hard bounces from last
   month's verification + campaigns -> bounces.csv
4. Append manual do-not-contact     -> dnc.csv

EVERY CAMPAIGN, BEFORE IMPORT
5. Upload campaign CSV + all four
   files to the Suppression Checker
6. Domain matching ON, free
   providers auto-excluded
7. Review domain matches (5 min,
   catches over-suppression like a
   7,000-employee enterprise where
   one person opted out)
8. Import the clean CSV only

Step 7 deserves a note: domain suppression has one legitimate false-positive class, very large companies where one individual's opt-out should not block a different division. The stats tiles make this visible: if domain matches look disproportionate, scan the suppressed-rows download (it includes the reason and matched domain per row) and re-add the rows you consciously want. Deliberate exceptions are fine; silent collisions are not. For the full unsubscribe plumbing between tools, see the unsubscribe sync guide.