Virtual fax, also known as Fax-over-IP or FoIP, automatically converts incoming faxes into PDF files and sends it to your email account. Furthermore, a fax can be sent by simply sending an email to your virtual fax.
Virtual fax utilizes T38 and requires a T38 capable VoIP Gateway as well as a T38 capable fax machine, fax card or fax software. Fax server software that supports T38, making unified communication available with a variety of features such as fax-to-email. Fax-to-email sends the fax directly through a VoIP gateway and converts it into an email, and vice versa. The fax-to-email feature does not require any additional fax hardware but your email address.
Unified communication (UC) is often also referred to as real-time communication (RTC). It describes the integration of real-time enterprise communication services such as instant messaging, presence information, IP telephony, mobility features including extension mobility and single number reach, conference calls, fixed-mobile convergence (FMC), desktop and data sharing, call control and speech recognition with non-real-time communication services such as unified messaging (integrated voicemail, email, SMS and fax). Simplified, unified communication allows you to send a message on one medium, and have this message received on another medium.
As fax data can not be sent through an IT network in the same way as voice communications, the T38 protocol describes how to do this. T38 is described in RFC 3362. It basically converts a fax to an image and sends it to another T38 fax device where it is converted back into an analog fax signal. T38 is supported by most VoIP Gateways and analog telephone adapters (ATAs).