With SMTP mail, you handle your own email service on your in-house server. The MX records (mail records) for your domain are simply pointed to the static IP of your server and your email is directed straight to the server. This means there is no need to log on to Local Domain servers to collect your email, and similarly when sending, you can relay out directly from your server.
When using your own server for email, Local Domains can provide you with a backup email server. This ensures that if your own server is offline for any reason, or if your internet connection fails, we simply collect your mail for you. When your server is back online, email is automatically forwarded back to you.