Monitoring Deliverability Across Multiple Sending Domains

The Multi-Domain Challenge

Agencies managing client domains, enterprises with brand portfolios, and SaaS companies with multi-tenant email all face the same problem: monitoring one domain is straightforward; monitoring 20+ requires systems.

Common failure modes:

• One domain's reputation crashes unnoticed for weeks
• DMARC reports pile up unread across domains
• Blacklist hits on secondary domains go unseen
• Authentication breaks silently on lesser-used domains

Multi-Domain Monitoring Architecture

Level 1: Free Stack (5-10 Domains)

Tools:

• Google Postmaster Tools (all domains)
• Microsoft SNDS (if using dedicated IPs)
• Centralized DMARC reporting (Postmark free tier)
• MXToolbox blacklist monitoring (manual checks)

Process:

• Weekly manual check of each domain in Postmaster Tools
• Weekly review of DMARC aggregate reports
• Monthly blacklist scan
• Spreadsheet tracking reputation status

Limitations: Manual, doesn't scale past ~10 domains.

Level 2: Paid Stack (10-50 Domains)

Tools:

• GlockApps Agency ($199/month) - inbox placement testing
• dmarcian Business ($200+/month) - DMARC aggregation
• MXToolbox Pro ($99/month) - blacklist monitoring
• Google Postmaster Tools (manual but supplementary)

Process:

• Automated inbox placement tests weekly per domain
• Daily DMARC report review in unified dashboard
• Automated blacklist alerts
• Weekly reputation check in Postmaster Tools

Level 3: Enterprise Stack (50+ Domains)

Tools:

• Validity Everest ($1,000+/month) - comprehensive deliverability
• Valimail or dmarcian Enterprise - DMARC at scale
• Custom monitoring via Datadog/Grafana
• Dedicated alerting infrastructure

Process:

• Real-time monitoring with automated alerts
• Dedicated deliverability team oversight
• Quarterly domain audits
• Incident response procedures per domain

Google Postmaster Tools at Scale

Adding Multiple Domains

Each domain requires separate verification:

1. Go to postmaster.google.com
2. Click "+" to add domain
3. Verify via DNS TXT record or existing verification
4. Repeat for each sending domain

Tip: Use a naming convention for the verification records:

TXT record: google-site-verification=client1_abc123
TXT record: google-site-verification=client2_def456

Monitoring Workflow

Create a checklist for weekly review:

Domain	Gmail Rep	Spam Rate	Auth Pass	Last Checked
client1.com	High	0.02%	99.8%	3/28
client2.com	Medium	0.15%	99.5%	3/28
client3.com	High	0.01%	100%	3/28

Flag any domain with:

• Reputation below High
• Spam rate above 0.1%
• Auth pass below 99%

Centralized DMARC Reporting

Setup

1. Choose DMARC aggregation service (dmarcian, Postmark, Valimail)
2. Get your reporting address (e.g., [email protected])
3. Update each domain's DMARC record:

_dmarc.client1.com TXT "v=DMARC1; p=quarantine; rua=mailto:[email protected]"
_dmarc.client2.com TXT "v=DMARC1; p=quarantine; rua=mailto:[email protected]"

All reports flow to one dashboard.

What to Monitor

Per-domain metrics:

• SPF pass rate
• DKIM pass rate
• DMARC alignment rate
• Unauthorized sender attempts

Cross-domain patterns:

• Which domains have lowest auth rates?
• Which domains see spoofing attempts?
• Are authentication issues correlated?

Practitioner note: Centralized DMARC reporting revealed one of my client's domains was being actively spoofed—2,000+ unauthorized emails per day. We would have missed it checking domains individually because the volume looked like noise distributed across reports.

GlockApps for Multiple Domains

Agency Plan Setup

1. Create GlockApps account (Agency tier: $199/month)
2. Add each domain/sending identity
3. Configure seed lists per domain
4. Set up scheduled tests

Testing Workflow

Option 1: Scheduled Auto-Tests

• Configure weekly tests per domain
• Receive alerts when inbox rate drops
• Review aggregate dashboard

Option 2: Pre-Campaign Testing

• Test before major campaigns
• Verify placement on critical domains
• Archive results for trend analysis

Dashboard Organization

Group domains by:

• Client (for agencies)
• Brand (for enterprises)
• Use case (marketing vs transactional)
• Risk level (new domains vs established)

Building a Custom Multi-Domain Dashboard

For operations needing unified visibility:

Data Sources

1. ESP APIs - delivery metrics per domain
2. Postmaster Tools - manual export or scraping
3. DMARC aggregation - API or exports
4. Blacklist monitors - API checks

Dashboard Structure

Overview Panel:

• Total domains monitored
• Domains with warnings
• Domains with critical issues
• Last update timestamp

Domain Health Table:

Domain	Delivery	Complaints	Reputation	Blacklists	Status
domain1.com	99.2%	0.02%	High	0	Healthy
domain2.com	97.1%	0.18%	Medium	1	Warning

Trend Charts:

• Aggregate delivery rate across all domains
• Complaint rate trends per domain
• Reputation distribution (how many High/Medium/Low)

Technology Options

Looker Studio (free):

• Google Sheets as data source
• Manual data entry or automated via Apps Script
• Limited but functional for <20 domains

Datadog/Grafana:

• Custom metrics ingestion
• Real-time monitoring
• Alert integration
• Requires engineering resources

Retool/Budibase:

• Low-code dashboard builder
• API integrations
• Custom workflows

Alerting Across Domains

Critical Alerts (All Domains)

Set up alerts for:

• Complaint rate > 0.1% on any domain
• Blacklist appearance on any domain
• Delivery rate < 95% on any domain
• Authentication pass < 99% on any domain

Per-Domain Alert Routing

Route alerts to appropriate teams:

• Client domains → client account manager
• Marketing domains → marketing ops
• Transactional domains → engineering

Alert Aggregation

Avoid alert fatigue:

• Consolidate similar alerts across domains
• Daily summary for non-critical issues
• Immediate alerts only for critical thresholds

Common Multi-Domain Problems

Problem 1: Orphaned Domains

Domains that stop being used but still exist—no one monitors them, but they can still be spoofed or damage brand reputation.

Solution: Quarterly audit of all domains. Remove or maintain proper DMARC policies on unused domains.

Problem 2: Inconsistent Authentication

Different domains have different auth configurations—some miss DKIM, some have SPF issues.

Solution: Standardized authentication checklist applied to all domains. Regular audit against checklist.

Problem 3: Reputation Contamination

One problem domain sharing infrastructure with healthy domains.

Solution: Isolate high-risk domains on separate IPs. Consider separate ESPs for different risk profiles.

If you're managing multiple sending domains and struggling to maintain visibility across all of them, schedule a consultation to design a monitoring system that scales with your operation.

Sources

• Google: Postmaster Tools
• dmarcian: Domain Management
• GlockApps: Agency Plan
• MXToolbox: Pro Monitoring

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v1.0 · March 2026