Adding chosen dropdown item to mail subject

Hi,

I’m using the following label and want the chosen dropdown item in the email’s subject but haven’t found a way how to do this. I tried 2 mail-tags but that didn’t work. Any suggestions?

<label> Topic*
    [select* topic "Question|[email protected]" "Jobs|[email protected]" "Offer|[email protected]" "Suggestion|[email protected]"] </label>