Correct configuration of inbound and outbound connectors is essential for reliable mail routing through the mxHERO platform.

This article explains:
    •    The mandatory use of the “Server” field
    •    When and how to use the “Relay Server” field
    •    The correct SMTP endpoints for inbound vs. outbound flows
    •    Required connector structure when both inbound and outbound routing are used
    •    Updated guidance on historical questions (Server, Relay Server, Rcpt Lookup, MX Lookup)

1. Mandatory Use of the “Server” Directive

The “Server” field is now mandatory for all tenants, even if the customer uses mxHERO only for outbound email processing.

Why is the “Server” field mandatory?

Because mxHERO is an email gateway, not a mailbox host.
After processing an inbound email, mxHERO must know exactly where to deliver it next.
If the “Server” field is empty, mxHERO has no authoritative delivery target—and will fall back to public DNS MX resolution, which can yield unpredictable results, especially in multi-tenant or hybrid environments.

Correct values for the “Server” field

You may specify:
    •    A Fully Qualified Domain Name (FQDN)
    •    An IP address

Recommended “Server” values based on mail system

Key rule: Whatever system ultimately receives the email must be defined as the “Server” value.
This applies even if mxHERO is used only for outbound (Relay) operations, to prevent future configuration conflicts.

2. “Relay Server” Directive (Optional)

The Relay Server field is optional, and is only required in cases where the customer intends to route outbound mail through an external or alternative gateway.

When should “Relay Server” be used?

Use it only when outbound emails processed by mxHERO must be forwarded through:
    •    A security gateway (TrendMicro, Cisco, Barracuda, etc.)
    •    A compliance or archive system
    •    A custom outbound relay
    •    A filtering appliance
    •    A partner-specific outbound flow

3. SMTP Endpoints: Correct Usage for Inbound vs. Outbound

mxHERO uses two official SMTP endpoints, each with a specific purpose.

Outbound SMTP Endpoint

Used when sending mail from the customer → mxHERO → external delivery.

Both addresses below are aliases and function identically:

smtp.mxhero.com
smtp-relay.mxhero.com

Use these ONLY for outbound connectors.

Inbound SMTP Endpoint

Used when customers send inbound mail to mxHERO for processing, before final delivery to their internal mail system.

smtp-in.mxhero.com

This must be used for all inbound connectors.

4. Required Connectors When Using Both Inbound and Outbound Routes

If the customer uses both inbound and outbound email flows through mxHERO:

➤ They must configure two separate connectors:
    1.    Inbound Connector
    •    Host: smtp-in.mxhero.com
    •    Attached to inbound rules
    •    Requires correct Server directive
    2.    Outbound Connector
    •    Host: smtp-relay.mxhero.com (or smtp.mxhero.com)
    •    Attached to outbound rules
    •    Optionally uses Relay Server if desired

Why two connectors?

Inbound and outbound paths perform fundamentally different tasks.
Without two connectors, routing will be ambiguous and may produce unexpected behavior.

5. Additional/Advanced Configuration

In the mxHERO Dashboard, under Organizations and Domains > Domains > Editing the domain property, you will still find:

What are the benefits of enabling Rcpt Lookup?

It ensures mxHERO only accepts mail for known, authorized recipients, adding a security layer.

Use cases for Rcpt Lookup: enable it when recipient validation is required to prevent unauthorized delivery.

What are the benefits of enabling MX Lookup?

MX Lookup instructs mxHERO to query DNS MX records instead of A records when determining the next hop.

When should I enable MX Lookup: enable MX Lookup only when the destination mail system changes dynamically or when DNS should determine the authoritative route.