Set Up Connectors Between Microsoft 365 and SmarterMail

Note: This setup is functional but skipping TLS can be risky and should only be used in trusted and controlled environments. Proceed with caution.

💡 Objective

To establish a working email flow between Microsoft 365 (M365) and SmarterMail without enforcing TLS, and ensure email delivery works both ways: from SmarterMail to M365 and vice versa.

🧰 Prerequisites

  • Access to Microsoft 365 Admin Center (Exchange Admin Console)

  • Access to SmarterMail Admin interface

  • Admin credentials for both platforms

  • MX Record should point to Microsoft 365

🔧 Step-by-Step Setup

1. Configure Connectors in Microsoft 365

Navigate to: Microsoft 365 Admin Center → Exchange Admin Center → Mail Flow → Connectors

Create Connector #1: From SmarterMail to Microsoft 365

  • From: Partner organization

  • To: Microsoft 365

  • Name: SmarterMail to M365

  • Connection security: Ignore TLS (for this case)

  • IP authentication: Add the public IP of your SmarterMail server (e.g., xxx.xxx.xxx.xxx)

  • Validation: Add test sender domain/email for verification

Create Connector #2: From Microsoft 365 to SmarterMail

  • From: Microsoft 365

  • To: Partner organization

  • Name: M365 to SmarterMail

  • Connection security: Ignore TLS

  • Route email using: Fully qualified domain name (FQDN) or IP address of SmarterMail (e.g., mail.customdomain.com or xxx.xxx.xxx.xxx)

🔐 Tip: Disabling TLS may cause Microsoft to throw warnings. You can still save the connector by confirming it’s a trusted route.

2. Configure SmarterMail Domain Settings

Login to your SmarterMail admin panel and go to: Manage → Domains → [YourDomain] → Email Settings

Key Settings:

  • Inbound Message Delivery: Set to External (use MX record)

  • Deliver locally if user exists: ✅ Enabled

  • Enable Greylisting: Optional but good for spam filtering

  • Sender Verification Shield: Optional for spoof protection

This ensures SmarterMail only delivers emails for local users and all other mail routes based on the domain’s MX record (which points to M365).

📡 MX Record Setup

  • MX Record of your domain should already point to Microsoft 365. That means all incoming email will hit Microsoft first.

  • SmarterMail acts as a relay or internal sender in this scenario.

🔄 How It Works:

Direction Flow Path Connector Used Outbound (SmarterMail → M365) SmarterMail → M365 → External SmarterMail to M365 Inbound (External → M365 → SmarterMail) External → M365 → SmarterMail (local users) M365 to SmarterMail

⚠️ Things to Watch Out For

  • Skipping TLS: This is okay for internal/testing environments, but not recommended for production unless behind VPN or trusted firewall.

  • IP Addressing: Ensure the IP you whitelist is static and properly configured.

  • Smart Host Trust: Without TLS, spoofing risk increases. Trust only static, known IPs.

  • Looping Risk: Avoid loop configs by using “Deliver locally if user exists” toggle correctly.

✅ Final Checks

  • Test sending from SmarterMail to a Microsoft 365-hosted user

  • Test replies from M365 to SmarterMail

  • Monitor headers to ensure correct flow and no TLS errors

🧠 Bonus Tip

If Microsoft 365 blocks or flags your connector, try the following:

  • Set the connector to accept mail only from specific IPs

  • Re-validate the connector using the verification option

  • Temporarily enable TLS for validation, then disable again

REFERENCES

PreviousHybrid Mail SetupNextHybrid Setup: G-Suite to M365

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