There is not a lot you can do in your script I'm afraid. All the security and restrictions concerning mail sending is done on the mail server.
To send an email you need to define the server (SmtpServer param) over which the mail is sent.
You (the account under which you invoke the Send-MailMessage cmdlet) will need to be authorised to connect to the mail server.
The station also needs to be allowed to send email via that mail server. The list of allowed servers to send mail might be restricted to avoid spamming.
If the mail can reach the to To address, depends if the mail server can find the route to the destination user's mail server/mailbox.
In PowerShell you just send it like this. After that it is the mail setup in your environment.