Whats the difference between using SMTP server and a PHP mail command?
The main difference with these is that if you are using SMTP there are less connections to the server. If you are sending via cron you will find that there is a slight increase in speed as there is a smaller overhead in regards to the connections. However, if your mail server is optimized in anyway then the server that is set up better will obviously increase your speed of sending. You should talk to your host to find out if mail server optimization is a service that they offer as the mail server is where your send speed will bottleneck.
