Use the Get-Content cmdlet to get the list of server names. Loop over that list of names and use Send-MailMessage for each item in the list.
Now, since it's impossible for a server to receive an e-mail, how will you associate the list of servers that require a reboot with the correct DL?
Does your SMTP server require the use of SSL? Authenticated or anonymous connections? Will the message be in HTML or plain text? Will each message require customization (e.g., to identify the server in question)?
I'm sure you'll find quite a few examples of scripts that read a file containing email addresses and that send e-mail to each one.
Right now, I think your problem lacks sufficient definition. At this point I don't think you know what you don't know!