PRTG – P12 Mail Server Monitoring with PRTG – Easy Setup Tutorial

Monitoring a mail system is not optional — it is critical.
If your mail server goes down, business communication stops immediately.

In this lab, we will Monitor Mail Server infrastructure using PRTG Network Monitor. The mail server model used is Mailcow running on Docker, but the monitoring logic applies to any custom-built Linux mail server.

This guide covers infrastructure monitoring, mail protocol validation, web interface health checks, and SSL certificate monitoring — all configured inside PRTG.

🧪 LAB Environment

Mail Server Model:

• Mailcow (Docker-based)

• Running on a Linux VM

The monitoring structure is identical for:

• Postfix + Dovecot

• Zimbra

• Exchange (with adjustments)

• Any custom SMTP/IMAP server

⚙️ Step 1 – Add Device in PRTG

Before adding sensors, first add the Mail Server VM as a device.

1. Add Device in PRTG

2. Enter SSH username/password
   (🔐 SSH Key authentication is recommended)

PRTG will use SSH to collect system-level metrics.

⚙️ Step 2 – Add Sensors

We divide monitoring into 4 logical layers:

• VM Infrastructure (Mandatory)

• Mail Core Services

• Web & Administration

• SSL & Security

I️⃣ VM INFRASTRUCTURE (MANDATORY)

Infrastructure monitoring ensures the mail server stays operational at the system level.

1️⃣ Ping

Function
• Check if the Mailcow VM is online

Threshold
• ❌ No need to set upper/lower
• DOWN on timeout

📌 Default PRTG configuration is sufficient.

2️⃣ SSH Load Average v2

Function
• Monitor total CPU load of the mail server

Channel used
• Load Average (1 min)

Threshold
• ⚠️ Upper WARNING: CPU core × 1.5
• ❌ Upper DOWN: CPU core × 2.5

📌 Example
• VM 2 cores →

• Warning: 3

• Down: 5

This ensures high CPU usage is detected before performance degradation impacts mail delivery.

3️⃣ SSH Memory Usage v2

Function
• Monitor RAM usage (Mailcow + Docker consumes significant memory)

Channel used
• Percent Available Memory

Threshold
• ⚠️ Lower WARNING: 20%
• ❌ Lower DOWN: 10%

📌 Important Note

Linux does NOT treat cache/buffer as fully used memory.
Cache/buffer memory will be released immediately when applications require it.

To verify real memory usage inside the VM, run:

This gives accurate insight into memory allocation.

4️⃣ SSH Disk Free v2

Function
• Monitor disk space

⚠️ If disk becomes full → Mail server stops functioning.

Channel used
• Free Space %

Threshold
• ⚠️ Lower WARNING: 15%
• ❌ Lower DOWN: 5%

Disk monitoring is mandatory for production mail systems.

II️⃣ MAIL CORE SERVICES

Now we validate mail protocol functionality.

5️⃣ SMTP (Port 25 / 587)

Function
• Verify mail server receives mail from external sources

Threshold
• ❌ No need to set
• DOWN if unable to connect

📌 Critical for inbound mail flow

Create an additional SMTP sensor for port 587.

6️⃣ SMTP Secure (465)

Still using SMTP sensor.

Function
• Verify secure mail sending (SSL enabled)

Threshold
• ❌ No need to set
• DOWN if SSL handshake fails

Ensures encrypted outbound mail is working properly.

7️⃣ IMAP Secure (993)

Sensor type: IMAP

Function
• Ensure users can receive mail (Outlook, Thunderbird, Mobile)

Threshold
• ❌ No manual setting required
• DOWN = users cannot retrieve mail

📌 Required for production environments.

III️⃣ WEB & ADMINISTRATION

Mail systems also depend on web interfaces for management and users.

8️⃣ HTTP Advanced – Mailcow UI

Function
• Check Mailcow administration interface availability

URL

Channel used
• Loading time (Total page load time)
Reference: Nginx / PHP / Mailcow backend

Threshold
• ⚠️ Upper WARNING: 4000 ms
• ❌ Upper DOWN: 10000 ms

Slow response may indicate backend or database issues.

9️⃣ HTTP Advanced – SOGo Webmail

Function
• Monitor SOGo webmail user interface

URL

Threshold
• ⚠️ Upper WARNING: 4000 ms
• ❌ Upper DOWN: 10000 ms

If DOWN, users cannot access webmail.

IV️⃣ SSL & SECURITY

Security monitoring is essential for encrypted communication.

🔟 SSL Certificate

Function
• Monitor SSL certificate expiration

Channel used
• Days to Expiration

Threshold
• ⚠️ Lower WARNING: 15 days
• ❌ Lower DOWN: 7 days

Disable the “Revoked” channel because Let’s Encrypt SSL is used.

📌 Note
SSL Let’s Encrypt: turn off revoke check.

Monitoring SSL prevents unexpected certificate expiration and service disruption.

📊 Why You Must Monitor Mail Server with PRTG

A mail system depends on multiple components:

• VM health

• CPU & RAM availability

• Disk capacity

• SMTP services

• IMAP services

• Web interfaces

• SSL validity

If any single layer fails, users experience:

• Mail delivery failure

• Login issues

• Webmail downtime

• Security warnings

By using PRTG to Monitor Mail Server, you gain:

• Real-time visibility

• Proactive alerting

• Early detection of resource exhaustion

• Faster troubleshooting

• Reduced downtime

🏁 Conclusion

Mail server monitoring must cover infrastructure, protocols, web access, and security layers.

In this tutorial, you configured:

• Ping monitoring

• CPU, RAM, and Disk sensors

• SMTP & IMAP validation

• HTTP web interface checks

• SSL certificate expiration alerts

With this structured PRTG setup, your Mailcow server — or any Linux-based mail system — becomes fully observable and production-ready.

A properly configured monitoring system ensures your organization never discovers mail issues from end users — you detect and resolve them first.