Sender reputation is invisible until it breaks. Gmail quietly routes you to spam. Amazon SES throttles your account. A client forwards your bounce report asking awkward questions.
The fix isn't better subject lines — it's not sending to bad addresses in the first place.
The Pre-Campaign Checklist
Run this before every outbound batch — agency outreach, newsletter, or product launch:
1. Verify the Full Audience
Not a spot check. Every address through SMTP verification:
- Bulk upload for CSV audiences
- Company Finder Verify for prospect lists
- API for automated pipelines
2. Send Only to Valid
Hard rule we enforce in our own mass mail:
| Status | Send? |
|---|---|
| valid | ✅ |
| catch_all | ❌ |
| risky / unknown | ❌ |
| invalid | ❌ |
Catch-all passes SMTP but bounces later — the #1 reputation killer on cold outreach.
3. Run Preflight Report
Select recipients → Verify selected → review:
18 sendable · 7 blocked · 25 checked
Blocked reasons shown per row. No surprises after SEND.
4. Check Suppression List
Ensure bounces, complaints, and verified-invalid addresses are suppressed. SES webhooks should auto-add hard bounces — never mail them again.
5. Remove Vendor Scrapes
Block platform domains accidentally scraped from tool pages:
klaviyo.com,mailchimp.com,hubspot.com,salesforce.com
These aren't prospects — they're vendor inboxes.
6. Match Email Domain to Website
info@widget.solutions for widgets.hr — domain mismatch flag. Fix the email or remove the row.
Reputation Math That Matters
| Metric | Safe zone | Danger zone |
|---|---|---|
| Hard bounce rate | < 2% | > 5% |
| Complaint rate | < 0.1% | > 0.3% |
| Catch-all in send | 0% | Any volume |
| List age without re-verify | < 90 days | > 6 months |
One bad campaign to 500 unverified addresses can take weeks to recover.
What We Learned From Agency Outreach
Running campaigns to email marketing agencies taught us:
- Catch-all on Google Workspace looks valid at SMTP — bounces at delivery
- Scraped vendor emails (
@klaviyo.com) always bounce - Preflight catches what list status labels miss (live re-verify at send time)
- Valid-only rules reduced bounce rate from ~8% to under 2%
Post-Campaign: Close the Loop
- Monitor SES bounce/complaint notifications
- Add bounces to suppression automatically
- Update Company Finder list statuses
- Re-verify remaining contacts before next batch
Tools on Email Validator
| Tool | Role |
|---|---|
| Bulk verify | Clean CSV before import to ESP |
| Company Finder | Build + verify prospect lists |
| Mass mail preflight | Last gate before send |
| Blacklist monitor | Watch domain/IP reputation |
Verify before you send — Start free →
Related: Clean Agency List Guide · Catch-All Mistakes