Resolving Mail Status 6 on CJ1W-ETN11 with CJ1G-CPU42H

Problem Overview

Engineers commissioning the Omron CJ1W-ETN11 Ethernet unit on a CJ1G-CPU42H PLC frequently report that the SMTP mail send function fails even when the unit is properly mounted, the I/O table is registered, and the trigger bit is pulsed. The classic symptom: the unit's Mail Status Word returns a non-zero value, with status 6 being among the most commonly observed. Because the ETN11 does not provide a local web interface, engineers must interpret this status code from the allocated CIO words and cross-reference it against the SMTP/TCP state machine inside the unit.

This reference documents the correct allocation, the meaning of status 6, the prerequisite network configuration, and the verification steps needed to bring the mail function online — both with a local on-site SMTP server and with an internet-hosted mail relay.

Prerequisites

• CJ1G-CPU42H (or compatible CJ1G/CJ1H CPU) with unit version 3.0 or later recommended for full ETN21/ETN11 compatibility.
• CJ1W-ETN11 Ethernet Option Board, mounted to the CPU or to an expansion rack slot.
• CX-Programmer (CX-One / Sysmac Studio) for the I/O table, Unit Setup, and CIO allocation.
• CX-Integrator (or the built-in ETN11 Setup Tool accessed through CX-Programmer) for IP, SMTP, and DNS parameters.
• Reachable SMTP server (local on-site mail relay or internet-hosted SMTP relay).
• Static IP address plan. The CJ1W-ETN11 does not support DHCP — every address must be programmed manually.

CIO Allocation for the ETN11

When the ETN11 is the first Ethernet unit on the rack (unit number 0), Omron allocates a fixed block of the CIO area to the unit. The relevant words are:

To send mail, the ladder or ST program must pulse CIO 1500.03 from OFF to ON while the ETN11 is idle (status 0). The bit must then be held ON until the status word transitions back to 0, or it can be turned OFF on the next scan after the trigger is acknowledged — implementation depends on the application.

Decoding Mail Status Word Value 6

The Mail Status Word in CIO 1501 reflects the SMTP state machine inside the ETN11. The interpretation of value 6 is one of the following, depending on firmware revision and on whether the unit completed the TCP three-way handshake to the SMTP server:

In practice, status 6 is reported when:

1. The DNS lookup of the SMTP server hostname fails (no DNS configured, or DNS server unreachable).
2. The TCP socket open to port 25 is refused or times out (firewall, wrong IP, wrong port, server offline).
3. The SMTP server disconnects during HELO/EHLO (server requires TLS on a port that the unit does not have configured, or the server does not accept plain-text auth).

Step-by-Step: Correct ETN11 Network and Mail Configuration

1. Open CX-Integrator and connect to the PLC online. The ETN11 must be registered in the I/O Table with its correct unit number (default = 0 for the first Ethernet unit).
2. Open the Unit Setup dialog for the ETN11. Select the unit in the Component List and double-click to launch the setup tool.
3. Configure the IP parameters (TCP/IP tab):
   • IP Address: a free static address on the LAN (for example, 192.168.1.50).
   • Subnet Mask: matches the LAN (typically 255.255.255.0).
   • Default Gateway: the router that provides internet access (for example, 192.168.1.1). If using a purely local SMTP server with no internet routing, set the gateway to a valid router on the same subnet anyway, or to 0.0.0.0 if the SMTP server is on the same subnet.
4. Configure DNS (TCP/IP > DNS tab):
   • Primary DNS server: the IP of the local DNS resolver (for example, 192.168.1.1, or the ISP-provided DNS).
   • Secondary DNS: optional but recommended for resilience.
   • If the SMTP server is referenced by IP address, DNS is still required for some authentication flows. If the SMTP server is referenced by hostname, DNS is mandatory.
5. Configure Mail (E-mail tab):
   • SMTP Server IP Address: the IP of the mail server. For a local on-site relay, this is the IP of the local server (for example, 192.168.1.20). For an internet relay, this is the public IP or the resolved IP of the relay host.
   • SMTP Port Number: 25 for plain-text, 465 for implicit TLS (not supported by ETN11), 587 for STARTTLS (not supported by ETN11). Most ETN11 firmware builds only support plain SMTP on port 25. Use a local relay or a TLS-stripping internet relay.
   • Source (From) E-mail Address: a valid sender on the mail server (for example, [email protected]).
   • Destination (To) E-mail Address: the recipient engineer address.
   • Login User Name / Password: required only if the SMTP server enforces AUTH LOGIN. Many local servers permit open relay on the LAN; internet-hosted SMTP almost always requires authentication.
   • Subject: a fixed string, optionally combined with a CIO/DM-mapped template using substitutions.
6. Download the unit setup to the ETN11. The unit must be restarted for some parameters to take effect. Power-cycle the PLC or reset the unit through the I/O Table.
7. Verify in the Mail Status Word that the unit returns to 0 after the restart — this confirms the setup was accepted.

Triggering the Mail Send from Ladder

A minimal example for CX-Programmer ladder:

|  P_On    |---------|  MailSendPulse   |  |  CIO 1500.03  |
|          |   |     |  (P_GT          |  | (rising edge) |
|  W150.01 |--|-------|  DM_status  0) |--+                |
|          |   |     |                |  |                |
|          |  _|     |                |  |                |
|          | | |     |                |  |                |

Where W150.01 is the application's mail event. The pulse must be a one-shot rising edge. Holding the bit ON continuously is a common commissioning mistake and will re-trigger the SMTP send every cycle of the unit's state machine, producing intermittent status errors.

Verification Procedure

1. Open CX-Programmer's Watch window. Monitor CIO 1501 (Mail Status Word) and CIO 1502 (Mail Send Result).
2. Trigger the bit. Within seconds, CIO 1501 should move through 1 → 2 → 3 → 4 → 5 and return to 0.
3. If the status returns to 0 and CIO 1502 is 0, the mail was accepted by the SMTP server. Check the recipient inbox (and the spam folder).
4. If CIO 1501 stops at 6, capture the value of CIO 1502 and look up the error in the ETN11 Operation Manual (W465).
5. Verify network path with a laptop on the same subnet: ping <ETN11 IP>, telnet <SMTP IP> 25. The telnet test must produce a 220 banner from the SMTP server.

Troubleshooting Matrix

Local SMTP Server vs. Internet Relay

The CJ1W-ETN11 has no built-in TLS, no OAuth support, and no DH-only authentication flow. In practice, two deployment patterns work reliably:

1. Local SMTP relay on site. A Windows Server, a Linux postfix/sendmail instance, or an industrial IoT gateway (for example, a Hirschmann, Moxa, or similar) runs an SMTP service that accepts plain-text mail from the PLC's IP and forwards it to the corporate Exchange/365 environment. This is the only practical way to keep all traffic on a sealed industrial network.
2. Internet SMTP relay with explicit IP allow-list. Services like Mailgun, SendGrid, or a corporate SMTP gateway can be configured to accept connections from the ETN11's static public IP. The ETN11 must be entered in the relay's allow-list. Because the ETN11 cannot do STARTTLS, the relay must accept plain SMTP on a non-standard port (for example, 2525) that is allowed through the corporate firewall.

Common Configuration Mistakes

• Leaving gateway 0.0.0.0 when an internet relay is used. Status 6 is the immediate result.
• Using a hostname for the SMTP server without configuring DNS. The unit will not fall back to netbios or local resolution.
• Typing the SMTP port as 465 or 587. The ETN11 will open a TCP socket to the port but cannot negotiate TLS; the server will close the connection, producing status 6.
• Assuming the unit retries automatically. The ETN11 makes one attempt per rising edge of bit 1500.03. The PLC program must re-trigger to retry.
• Failing to register the PLC's sender address in the mail server. Many servers (especially Exchange/365 in default config) reject mail from unknown senders, producing status 6 after the EHLO step.

Field-Proven Commissioning Tip

Before commissioning the PLC, set up a laptop on the same subnet, configure it with the same IP, gateway, and DNS that you intend to program into the ETN11, and run ipconfig /all (Windows) or nmcli (Linux) to validate the values. Then attempt a manual SMTP transaction from the laptop with telnet <smtp_ip> 25 and a raw HELO/MAIL FROM/RCPT TO sequence. Only when the laptop path works should the same parameters be downloaded to the ETN11. This eliminates the network layer as a variable and isolates any subsequent failure to the unit's SMTP implementation or the application program.

Frequently Asked Questions