sending to two different recipients

Hi, I ask you for a little support. I need to send an information request to two different recipients, the choice is made with a drop-down menu. This is the form code:

<label> Il tuo nome (richiesto)
[text* your-name] </label>
<label> La tua email (richiesto)
[email* your-email] </label>
<label> Oggetto
[text your-subject] </label>
<label> Quale Istituto vuoi contattare?
[select your-recipient “Istituto professionale M.Polo|[email protected]”
“Istituto Tecnico C.Cattaneo|[email protected]”]</label>
<label> Il tuo messaggio
[textarea your-message] </label>
[submit “Invia”]

In the “Mail” section in the To: field, I entered the tag
[Your-recipient] <[email protected]>, <[email protected]>

Unfortunately, once the form has been completed with the choice of one of the recipients, the mail arrives to both. How can I change to make sure that by not choosing a recipient the message does not arrive at both?

Thanks for the attention

The page I need help with: [log in to see the link]