VI using SMTP email library has different behaviour on different machines

[DakotaD]

I have a VI that uses the LabView SMTP email library that exhibits different behaviour when executed on just one machine, the other six machines that use this VI have no problems.

Using Wireshark it looks like the problem is the VI is asking the email server to verify the email address it is sending to, while on the other machines the VI skips this step.

Here is the VI with the inconsistant behaviour:

It can been seen in the screen capture from Wireshark below that this VI is using the VRFY command which causes the email to fail:

The communication sequence that correctly sends an email from other machines is seen below, note the lack of the VRFY command:

For comparison I wrote another simple email sending VI using the .NET controls, this VI successfully sends emails from the problematic machine.

[tst]

I have no idea what the answer is (no real experience with SMTP), but it looks like the SMTP VIs actually use a DLL in the resource folder to do their work. My guess is that this DLL probably calls a system DLL and on that computer it has different functionality for some reason. You might be able to use a tool like Dependency Walker to see which DLLs it calls.

The practical option might be to use the .NET code.