The restriction isn't so much a Universal Email one, it is a restriction on the server end.
there are a number of factors, most notable the Number Of Concurrent connections the email server can handle. and the time for a script to time out.
The email server will need to be able to handle a connection for each recipient. If you are mailing to 800 people, it will need to allow over 800 concurrent connections. Probably more like 850 or 900, there will be others using the SMTP server as well.
To send to that many people, the script will likely run for a while, the Script timeout setting will need to increased to account for that.