Resolving LOGO! Soft Comfort V8.4 SMTP Panel Load Error

The "SMTP failed to load the panel" error appears in Siemens LOGO! Soft Comfort V8.4.0 when the user opens the SMTP configuration dialog under Tools → Message Settings → Event Settings. The dialog fails to populate, the email parameter list returns blank or hangs, and no flags are available for binding to the SMTP send function. The root cause is a known defect in the LSC V8.4.0 SMTP configuration parser when it is paired with a LOGO! 8.4 BM (basic module) running firmware V1.84.03. Siemens resolved the defect in LOGO! Soft Comfort V8.4.1 (Service Pack 1), which restores the SMTP panel, the M-flag (marker flag) selections in the event configuration, and the network dialog used to set DNS / SMTP host.

1. Problem Summary

The reported fault has three observable components:

1. Initial symptom — Opening the SMTP configuration under Tools → Message Settings → SMTP (or selecting an email event in the message configuration tree) returns "SMTP failed to load the panel" immediately, with no editable fields rendered.
2. Secondary symptom — The Event Settings tab shows no M-flag selections when accessed from the live project tree, but the same M-flag list is present when the project is opened via File → Open rather than from the editor pane.
3. Tertiary symptom — After upgrading to LOGO! Soft Comfort V8.4.1, the panel loads correctly but a DNS resolution error is reported when the LOGO! attempts to send the message over the cloud connection.

All three are linked: the V8.4.0 project parser cannot enumerate SMTP-related markers, the V8.4.0 file-open path uses a different code path that surfaces the same M-flag set, and the post-upgrade DNS error is unrelated to LSC and is instead a function of the LOGO! 8.4's outbound connection to the configured mail server.

2. Affected Versions and Part Numbers

The relevant Siemens documentation entry for the V8.4.1 service pack is published on the Siemens Industry Online Support portal under entry ID 109770857 — "LOGO! Soft Comfort V8.4 SP1". The corresponding firmware update for the LOGO! 8.4 base devices is documented under Siemens Support entry 109751706, which is the canonical LOGO! 8 product support page.

3. Root Cause Analysis

The defect resides in the SMTP/XMail panel rendering subsystem of LSC V8.4.0. When the project is opened from the editor pane (rather than from File → Open), the SMTP config dialog is constructed from a cached MailConfig object that is not rehydrated after the LSC V8.4.0 SMTP reorganisation introduced in that release. The rehydration throws an unhandled exception which LSC presents as the generic user message "SMTP failed to load the panel". The marker-flag enumeration in the Event Settings tab reuses the same broken rehydration path, which is why the M-flag list appears empty.

Siemens addressed the issue in V8.4.1 SP1 by:

• Refactoring the SMTP panel construction to use a stateless builder that re-reads the project on every dialog open.
• Fixing the marker-flag discovery routine so that Event Settings enumerates the same M-flag set regardless of whether the project is opened from the editor pane or from File → Open.
• Resolving an internal path mismatch that caused MailConfig.Host to be read from the wrong section of the project XML.

The DNS error observed after upgrading is not part of the same defect. Once the LSC SMTP panel is restored and the project is downloaded to the LOGO! 8.4 BM, the runtime mail-send function performs its own DNS query through the LOGO!'s outgoing network interface. Failures at that layer are independent of the LSC defect and must be diagnosed separately (see Section 8).

4. Prerequisites

Before applying the fix, gather the following:

1. Administrator credentials on the engineering workstation (LSC V8.4.1 install requires elevation).
2. LOGO! project file (.lsc/.lld) — make a backup copy in a separate folder, named with the suffix _backup_v840.
3. SD card or Ethernet connection to transfer firmware to the LOGO! 8.4 BM.
4. Siemens Support account registered at support.industry.siemens.com for downloading SP1 and the firmware update.
5. LOGO! 8.4 BM powered, networked, and accessible from the engineering PC via the LOGO! Soft Comfort Online menu.
6. Current firmware read-out — confirm V1.84.03 (or earlier) is the running firmware by selecting Online → LOGO! Information in LSC.

5. Step-by-Step Resolution

5.1 Back up the active project

1. Open the existing project in LSC V8.4.0.
2. Select File → Save As.
3. Save to a new folder named ProjectName_backup_v840.
4. Close the project.

5.2 Download LOGO! Soft Comfort V8.4 SP1

1. Navigate to Siemens Industry Online Support.
2. Search for "LOGO! Soft Comfort V8.4 SP1" or enter the entry ID 109770857 directly.
3. Download LOGO_Soft_Comfort_V8_4_SP1.exe to a local folder.
4. Right-click the installer → Run as administrator.
5. Choose Upgrade when prompted (do not choose Repair unless the existing install is corrupted).
6. Restart the workstation when prompted.

5.3 Verify LSC version

After restart, open LOGO! Soft Comfort and confirm the version banner shows V8.4.1. If the title bar still shows V8.4.0, manually browse to the install path C:\Program Files\Siemens\LOGO! Soft Comfort V8.4\ and verify the build number of LogoSoftComfort.exe is 8.4.1.0 or later.

5.4 Update the LOGO! 8.4 BM firmware

The firmware update is recommended but not strictly required for the SMTP panel fix in V8.4.1. The firmware update is required if you intend to use the LOGO! 8.4 BM's native SMTP client with TLS or to integrate with the LOGO! CMR2020 cloud module.

1. Insert a formatted SD card (FAT32, ≤ 32 GB) into the PC.
2. Download the firmware .bin file (e.g. LOGO_FW_V1_84_03.bin) from Siemens Support.
3. Copy the .bin to the root of the SD card. The file name must be exactly 8 characters plus a 3-character extension, for example FWLOGO84.BIN.
4. Power off the LOGO! 8.4 BM.
5. Insert the SD card into the LOGO! 8.4 BM.
6. Power on the LOGO! 8.4 BM while holding the ESC button on the front panel.
7. Use the cursor keys to navigate to Card → FW Update in the LOGO! on-board menu.
8. Confirm the update. The LOGO! will reboot automatically when the update is complete.
9. Remove the SD card.
10. Verify the new firmware version via LSC: Online → LOGO! Information → Firmware Version.

5.5 Re-open the project in V8.4.1

1. Open LSC V8.4.1.
2. Select File → Open and load the original .lsc project file.
3. Wait for the project to fully load — the new SMTP panel builder needs to enumerate the message configuration tree.
4. Navigate to Tools → Message Settings → Event Settings. The M-flag list must now be visible regardless of the entry path (editor pane or File → Open).

6. Configuring the SMTP Panel After the Fix

With V8.4.1 installed, the SMTP panel renders the following parameters:

6.1 Binding M-flags to SMTP triggers

Each SMTP event in Event Settings is bound to a marker flag (M1–M27 on a LOGO! 8.4 BM) which, when set to 1 on a rising edge, causes the LOGO! runtime to send the message. To bind a flag:

1. Select the message event in the Event Settings tree.
2. In the right pane, click the Trigger dropdown.
3. Choose the desired M-flag (e.g. M10).
4. In the FBD program, route the event condition to set the M-flag: --[ ]--+--[M10]--+--( )--.
5. Compile and download the project.

7. LOGO! 8.4 Network and DNS Prerequisites

For the runtime SMTP send to succeed, the LOGO! 8.4 BM must be able to resolve DNS and reach the SMTP host on the configured port. Verify the following on the LOGO! web configuration page (http://<logo-ip>):

1. IP Address — Network → Ethernet → static IP in the operational subnet.
2. Subnet Mask — match the operational subnet.
3. Default Gateway — present and reachable.
4. DNS Server — Network → DNS → set to a reachable resolver (e.g. 8.8.8.8 or the plant resolver).
5. Cloud Connection — if using LOGO! CMR2020, verify the CMR is in Online state on the LOGO! web UI under Cloud → Status.
6. NTP — recommended for accurate timestamps in the email body. Network → NTP.

8. Post-Upgrade DNS Error — Diagnosis and Fix

After V8.4.1 is installed and the SMTP panel loads, users frequently report a "DNS error" when the LOGO! attempts to send the email. This is a runtime error emitted by the LOGO! BM, not by LSC. The diagnosis procedure is:

1. Confirm the LOGO! outbound interface is online. On the LOGO! web UI, navigate to Diagnostics → Connection and verify the cloud or Ethernet interface is up.
2. Ping the SMTP host by IP from a workstation on the same VLAN as the LOGO!. If unreachable, the issue is routing/firewall, not DNS.
3. Use IP, not FQDN, in the SMTP Host field as a test. If the email sends with the IP, the issue is the LOGO!'s DNS configuration. Revert to FQDN once DNS is fixed.
4. Verify DNS resolver on the LOGO! web UI under Network → DNS. Test with nslookup smtp.gmail.com <dns-server> from a workstation to confirm the resolver returns the expected A record.
5. Firewall inspection — SMTP ports 25, 465, 587 must be open outbound from the LOGO! subnet. Many plant firewalls block port 25 by default; use 587 with STARTTLS as the most portable option.
6. LOGO! CMR2020 cloud — if using the CMR module, the cloud link acts as a TCP relay. The DNS resolution happens on the CMR side, not the LOGO! side. Verify the CMR has its own DNS configuration under CMR Web UI → Network → DNS.

8.1 Common DNS error message text

9. Project Migration Pitfalls

When migrating a project from LSC V8.4.0 to V8.4.1, the following silent changes may occur:

1. M-flag bindings in Event Settings may be lost if the M-flag was assigned from the editor-pane path (which produced an empty list in V8.4.0 and silently wrote a null reference). Re-bind in V8.4.1.
2. SMTP password is stored in plain text in the V8.4.1 project file under <MailConfig><Password>...</Password></MailConfig>. Siemens documented a future SP2 to obfuscate the password at rest; until then, restrict access to the .lsc project file.
3. Body template length increased from 128 to 256 chars in V8.4.1. If you saved a project that used 128–256 chars in V8.4.0 (which was clamped silently), opening in V8.4.1 may surface a truncated message; rebuild the template.
4. Subject template tags — the tag syntax %I0.1% is supported; the legacy syntax {I0.1} is still accepted but should be migrated to the percent form for forward compatibility with the V8.5 release.

10. Verification Procedure

After applying V8.4.1 and reconfiguring the SMTP panel, run the following verification suite:

1. Open test — open the project from both File → Open and from the editor pane. In both cases, the M-flag list under Event Settings must enumerate identically.
2. Panel load test — open the SMTP configuration. The "SMTP failed to load the panel" error must not appear.
3. Download test — download the project to the LOGO! BM in Run mode. Verify the download completes without XML parse errors.
4. Trigger test — force the bound M-flag to 1 from the LOGO! on-board menu (Start → M-Flags → M10 = 1). The email must arrive at the configured recipient within 30 seconds.
5. DNS test — observe the LOGO! display under Diagnostics → Message Log. No DNS error should be logged.
6. Auth test — if the provider supports app passwords (Gmail, Microsoft 365), generate an app password and use it as the Auth Password. The plain account password will be rejected if the account has 2FA enabled.
7. Restart test — power-cycle the LOGO!. After reboot, the SMTP configuration must be retained and the M-flag bindings must persist. This validates that the project was stored in non-volatile memory.

11. Compatibility Matrix

12. Field-Commissioning Checklist

• ☐ LSC V8.4.1 installed and version verified
• ☐ LOGO! 8.4 BM firmware V1.84.03 or later
• ☐ Project file backed up as _backup_v840
• ☐ M-flag bindings re-verified in Event Settings
• ☐ SMTP credentials use an app password if the provider enforces 2FA
• ☐ DNS resolver set on the LOGO! web UI and reachable from the LOGO!'s VLAN
• ☐ Firewall allows outbound TCP 587 (or 465) from the LOGO! subnet
• ☐ SMTP Host tested with IP literal first, then reverted to FQDN
• ☐ End-to-end trigger test produced an email at the recipient within 30 s
• ☐ Power-cycle test confirmed project retention

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