Is there a difference between smtpsocket and smtpsecuresocket with secure=false ?

everything is in the title.
I have an app sending emails with smtpsocket, which is deprecated.
so replacing it with smtpsecuresocket, as the customer’s smtp is still not secure, I set the secure property to false.
it seems the mail is sent, no error, but some recipients get it and some don’t get it.

is there any difference between smtpsocket and smtpsecuresocket with secure=false (and port=25) ?
thanks.

edit: the connectiontype is set to tls12 and the the smtpconnectionmode is set to starttls