Postal + GoHighLevel Integration: SMTP Setup

Why Postal for GoHighLevel

Postal is an open-source mail server designed for transactional and marketing email. Unlike Mailcow (which is a full email suite), Postal focuses on sending — which makes it a clean fit for GoHighLevel agencies that need SMTP relay without mailbox management.

For Mailcow-based integration, see our Mailcow + GHL guide. For general GHL SMTP setup, see our GoHighLevel SMTP guide. Key advantages over Mailgun for GHL agencies:

• Flat cost: $5-10/month VPS vs per-email Mailgun pricing
• Built-in tracking: Open tracking, click tracking, delivery status per message
• Multi-organization: Each client gets isolated credentials and metrics
• Web UI: Visual message logs, not just API responses

Prerequisites

Before connecting to GHL:

1. Postal is installed and running (setup guide)
2. DNS is configured — SPF, DKIM, DMARC for your sending domain(s)
3. Your VPS IP is clean — check blacklists with MXToolbox
4. Port 25 is open on your VPS

Step 1: Create an Organization

In Postal's web UI:

1. Click Organizations → New Organization
2. Name it (e.g., "Agency Name" or "Client Name")
3. Save

Organizations in Postal isolate sending credentials, domains, and statistics. Use one per client or per GHL sub-account.

Step 2: Create a Server

Within the organization:

1. Click Servers → New Server
2. Name it (e.g., "GHL Sending" or "Client-Marketing")
3. Save

Step 3: Add a Domain

In the server settings:

1. Go to Domains → Add Domain
2. Enter the sending domain (e.g., clientdomain.com)
3. Postal shows required DNS records — add them all:
   • SPF include or IP authorization
   • DKIM TXT record (Postal generates the key)
   • Return-path CNAME

Verify the domain in Postal after DNS propagation.

Step 4: Generate SMTP Credentials

1. Go to Credentials → Add Credential
2. Postal generates a username and key
3. Copy these — they're your SMTP authentication

Important: Postal credentials are per-server. Each server can have multiple credentials for different applications.

Step 5: Configure GoHighLevel

In GoHighLevel:

1. Go to Settings → Email Services → Add SMTP
2. Enter:

Field	Value
SMTP Host	postal.yourdomain.com
SMTP Port	25
Username	(from Postal credential)
Password	(from Postal credential)
Encryption	STARTTLS

3. Test the connection
4. Save and assign to the sub-account

Practitioner note: Postal defaults to port 25 for SMTP submission, which works but some networks block it. If you need port 587, configure it in Postal's config file. Most GHL setups work fine on port 25 since the connection is server-to-server, not through an ISP that might block outbound port 25.

Multi-Client Agency Setup

For agencies managing multiple GHL sub-accounts:

Option A: One Organization Per Client

Postal Server
├── Organization: Client A
│   ├── Domain: clienta.com
│   ├── Credentials: clienta-smtp
│   └── Separate tracking/stats
├── Organization: Client B
│   ├── Domain: clientb.com
│   ├── Credentials: clientb-smtp
│   └── Separate tracking/stats
└── Organization: Client C
    └── ...

Each client gets their own credentials in GHL. Domain reputation is per-domain, so one client's poor practices don't affect DNS records for others (though they share the same IP).

Option B: One Organization, Multiple Domains

Simpler for agencies that want centralized management:

Postal Server
└── Organization: My Agency
    ├── Domain: clienta.com
    ├── Domain: clientb.com
    ├── Domain: clientc.com
    └── Credentials: agency-smtp

All clients use the same credential but send from their own domains. Less isolation but easier to manage.

Practitioner note: I always use Option A for agencies. The per-organization isolation in Postal means you can show each client their own sending statistics without exposing other clients' data. It also makes it easy to disable a specific client's sending without affecting others.

Postal vs Mailcow for GoHighLevel

Feature	Postal	Mailcow
Primary purpose	Sending/relay	Full email suite
Message tracking	Built-in (opens, clicks)	No built-in tracking
Multi-org support	Native	Via domains/mailboxes
Webmail	No	Yes (SOGo)
RAM required	2GB	2GB
Best for	Agencies sending through GHL	Businesses needing full email

For pure GoHighLevel SMTP relay, Postal is the better fit. You get per-message tracking, organization isolation, and a web UI designed for sending operations. Mailcow includes a lot of features (webmail, calendar, contacts) that GHL agencies don't need.

Troubleshooting

Connection Refused

Check that port 25 is open on your VPS firewall and that Postal's SMTP service is running:

docker compose logs postal-smtp

Authentication Failed

Verify the credential is active in Postal and the username/password match exactly. Postal credentials are case-sensitive.

Emails Going to Spam

Check in order: PTR record, SPF record includes server IP, DKIM record matches Postal's generated key, DMARC record exists. Use Postal's message inspector to see authentication results per message.

Practitioner note: Postal's message log is its killer feature for troubleshooting. Click any message and see the full delivery log — SMTP conversation, authentication results, receiving server response. When a GHL client says "my email went to spam," you can pull up the exact message and see why in 30 seconds.

If you want Postal set up and optimized for your GoHighLevel agency, schedule a consultation — I deploy Postal infrastructure for agencies that want self-hosted sending with professional tracking.

Sources

• Postal: Documentation
• Postal: GitHub Repository
• GoHighLevel: Custom SMTP Documentation
• Hetzner: Cloud Servers

---

v1.0 · April 2026