E-mail on file transfer failure?

I would like to know how to modify an existing script so it will send an e-mail if a file transfer is unsuccessful. I think I found the command that generates the e-mail but I don't know what it takes to identify and set the flag that says the file failed to transfer.

Any help would be appreciated as I am usually not a programmer.

Thanks.

Please read documentation:
https://winscp.net/eng/docs/script_email