In our SMTP Server, you can choose, which type of authentication is needed for your users. The simplest one for you, is not to have any authentication at all, but we highly recommend that you do not enable it.
If you disable all authentication, and your server is located on the open Internet (not intranet), then it will be used by spammers to relay spam messages. Only use that setting, if your server is installed purely on the intranet.
Most of our customers use the third authentication type, which will allow you to specify local IP ranges and let everybody else authenticate. For example, in a corporation, all local IP addresses will be listed and any person from within the organization will be able to relay freely, but any person coming from the outside, will need to login first.