For GHL agencies: each client sub-account must have its own sending domain with its own SPF, DKIM, DMARC authentication and its own SMTP credentials. Never share one SMTP account across clients. If Client A's list triggers complaints, it should only affect Client A's reputation — not Client B's. Use one SMTP provider account (Mailgun, SendGrid) with separate domains verified per client. Monitor each domain independently via Google Postmaster Tools.
GoHighLevel Agency Email Management: Per-Client Infrastructure Setup
The Agency Architecture
Your Mailgun/SendGrid Account
├── Client A (clienta.com)
│ ├── SMTP credentials for clienta.com
│ ├── [SPF, DKIM, DMARC](/gohighlevel-email/gohighlevel-email-authentication) on clienta.com
│ └── GHL Sub-Account A → uses clienta.com SMTP
├── Client B (clientb.com)
│ ├── SMTP credentials for clientb.com
│ ├── SPF, DKIM, DMARC on clientb.com
│ └── GHL Sub-Account B → uses clientb.com SMTP
├── Client C (clientc.com)
│ └── ... same pattern
One provider account. Multiple domains. Isolated credentials. Isolated reputation.
Per-Client Setup Checklist
For each new client sub-account:
1. Domain Setup
- Verify client's sending domain in SMTP provider (Mailgun/SendGrid)
- Add SPF include for SMTP provider to client's DNS
- Configure DKIM (add DNS records from SMTP provider)
- Publish DMARC record on client's domain
- Set up custom tracking domain (links.clientdomain.com)
2. SMTP Credentials
- Create dedicated SMTP credentials for this domain in SMTP provider
- Enter credentials in client's GHL sub-account (Settings → Email Services)
- Test: send from GHL, verify authentication passes in email headers
3. Monitoring
- Set up Google Postmaster Tools for client's domain
- Add client's sending IPs to blacklist monitoring
- Document SMTP credentials in agency credential management system
- Set calendar reminder for monthly deliverability check
4. Warmup
- New domain? Follow GHL warmup guide
- Start with 50-100 emails/day to client's most engaged contacts
- Increase over 3-4 weeks
- Don't launch bulk campaigns until warmup is complete
Scaling Considerations
5-10 Clients
- One Mailgun Foundation ($35/mo) or Scale ($90/mo) account
- Manual monitoring via Postmaster Tools per domain
- Monthly deliverability check per client
10-25 Clients
- Mailgun Scale or Custom plan
- Consider self-hosted SMTP (Postal) for cost savings
- Automated monitoring with HetrixTools + n8n alerts
- Bi-weekly deliverability review
25+ Clients
- Self-hosted SMTP strongly recommended (cost at scale)
- Postal multi-organization architecture maps to per-client management
- Automated blacklist monitoring, bounce processing, and alerting
- Dedicated infrastructure monitoring workflow
Cost Comparison at Agency Scale
| Clients | Total Volume | Mailgun | Self-Hosted (Postal) | Annual Savings |
|---|---|---|---|---|
| 5 | 50K/mo | $35/mo | $10/mo | $300/yr |
| 10 | 100K/mo | $90/mo | $10/mo | $960/yr |
| 20 | 200K/mo | $175+/mo | $15/mo | $1,920/yr |
| 50 | 500K/mo | $275+/mo | $20/mo | $3,060/yr |
At 20+ clients, self-hosted SMTP saves $1,920+/year with better control.
What Not To Do
Never share one sending domain across clients. If Client A sends spam from shared-domain.com, Client B's campaigns from the same domain go to spam too.
Never use LC Email for client accounts. Shared Mailgun infrastructure across all GHL users. No reputation isolation. No monitoring. Unacceptable for agency clients.
Never skip authentication. Every client domain must have SPF, DKIM, DMARC. A client sending unauthenticated email damages their domain permanently.
Never skip warmup. Even if the client "needs to send immediately." Burning a domain in week 1 costs more time than the 3-4 week warmup.
Practitioner note: The agencies I work with that have the best client retention all have one thing in common: per-client email infrastructure isolation. When you can show a client their own domain reputation dashboard, their own delivery metrics, and their own authentication status — that's a service offering. Not a commodity.
Practitioner note: For agencies just starting with custom SMTP: begin with Mailgun (simplest setup per domain, good GHL compatibility). Once you hit 15-20 clients, evaluate Postal (self-hosted). The migration is straightforward — change SMTP credentials in each sub-account.
If you want agency email infrastructure designed and deployed across your client base, schedule a consultation — I build per-client email architecture for GHL agencies.
Sources
- Mailgun: Domain Management
- GoHighLevel: Sub-Account Management
v1.0 · March 2026
Frequently Asked Questions
Should each client have their own sending domain?
Yes, absolutely. Each client should send from their own branded domain (client.com or marketing.client.com) with their own authentication records. This isolates reputation between clients. If one client's sending damages their domain, your other clients are unaffected.
Can I use one Mailgun account for all clients?
Yes — one Mailgun account with multiple verified domains. Each client's domain is verified separately in Mailgun with its own SPF, DKIM, and SMTP credentials. The billing is centralized but the sending infrastructure is isolated per domain.
How do I monitor deliverability per client?
Set up Google Postmaster Tools for each client's sending domain. Check each domain's reputation independently. In your SMTP provider dashboard, filter analytics by sending domain to see per-client delivery metrics.
What happens if a client has a bad list?
With proper isolation: only that client's domain reputation suffers. Without isolation (shared domain or shared SMTP): all clients on the same infrastructure are affected. This is why per-client domain isolation is mandatory for agencies.
How many clients can one SMTP account handle?
Technically unlimited (Mailgun, SendGrid support many domains per account). Practically, your SMTP plan needs to cover total volume across all clients. At 10 clients averaging 10K/month each, you need a plan supporting 100K/month.
Want this handled for you?
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