How can one send a fax over the internet?

There are two ways to fax through the internet: Fax over IP, and an internet fax service.

Fax over IP is a system based on the ITU T.38 standard that allows faxing over IP in real time. For this to work, you would need to fax machines compatible with the T.38 standard.

An online fax service is hosted by a fax service provider, and works very much like a webmail service like hotmail or gmail does - it sends and receives faxes for you, and does so from a system hosted by the provider instead of through a fax machine sitting in your office.