Network LIB 1.30 SMTP: Resolving the Step 50 Error

On a Beckhoff CX running TwinCAT, the SMTP client worked with Network LIB 1.21 but stalled after upgrading to Network LIB 1.30. The reported diagnostics were ERROR_T: 0x05 and ERROR_C: 0x003200FA at step 50 with response code 250. The failure was reproduced with two SMTP servers.

Identify the Network LIB 1.30 failure

At step 50, the revised logic advances only when auth_state <> BYTE#0. In the failing case, auth_state remained 0x0, so the SMTP sequence could not continue.

Correct the authentication-name declaration

The confirmed cause was a test modification left in the function block. Each authentication name had an extra x, preventing the block from matching the advertised authentication methods and setting auth_state.

(* Incorrect Network LIB 1.30 test declaration *)
auth_names : STRING := ' PLAINx; LOGINx; CRAM-MD5x';

(* Correct declaration *)
auth_names : STRING := ' PLAIN; LOGIN; CRAM-MD5';

Apply and verify the correction

1. Open the SMTP client function block and inspect the auth_names declaration.
2. Remove the appended x characters, or replace the affected library with a corrected build.
3. Rebuild and run the SMTP transaction while monitoring auth_state, the step number, ERROR_T, and ERROR_C.
4. Confirm that auth_state no longer remains 0x0, execution advances beyond step 50, and the message transaction completes.

If the declaration is already correct but the sequence still stops, capture the SMTP exchange and compare the server response with the authentication names processed by the block. The evidence does not identify a specific corrected library version, so verify the declaration rather than relying on a version label alone.

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